Docs explanation for unassigned shard reason codes.
Docs explanation for unassigned shard reason codes.

Fixes #14001
Closes #15912

tebriel/elasticsearch,LewayneNaidoo/elasticsearch,mapr/elasticsearch,geidies/elasticsearch,wangtuo/elasticsearch,jbertouch/elasticsearch,rlugojr/elasticsearch,davidvgalbraith/elasticsearch,mikemccand/elasticsearch,mortonsykes/elasticsearch,pozhidaevak/elasticsearch,nomoa/elasticsearch,nezirus/elasticsearch,vroyer/elassandra,markwalkom/elasticsearch,mjason3/elasticsearch,gingerwizard/elasticsearch,StefanGor/elasticsearch,episerver/elasticsearch,scorpionvicky/elasticsearch,mortonsykes/elasticsearch,jchampion/elasticsearch,diendt/elasticsearch,MaineC/elasticsearch,strapdata/elassandra5-rc,gfyoung/elasticsearch,nknize/elasticsearch,rajanm/elasticsearch,girirajsharma/elasticsearch,IanvsPoplicola/elasticsearch,nomoa/elasticsearch,yanjunh/elasticsearch,Helen-Zhao/elasticsearch,LewayneNaidoo/elasticsearch,scottsom/elasticsearch,fernandozhu/elasticsearch,njlawton/elasticsearch,rlugojr/elasticsearch,Shepard1212/elasticsearch,sneivandt/elasticsearch,Stacey-Gammon/elasticsearch,geidies/elasticsearch,yanjunh/elasticsearch,nezirus/elasticsearch,elasticdog/elasticsearch,ESamir/elasticsearch,glefloch/elasticsearch,IanvsPoplicola/elasticsearch,dongjoon-hyun/elasticsearch,mjason3/elasticsearch,jimczi/elasticsearch,scottsom/elasticsearch,fforbeck/elasticsearch,umeshdangat/elasticsearch,davidvgalbraith/elasticsearch,sreeramjayan/elasticsearch,dpursehouse/elasticsearch,gingerwizard/elasticsearch,nilabhsagar/elasticsearch,kalimatas/elasticsearch,scottsom/elasticsearch,i-am-Nathan/elasticsearch,robin13/elasticsearch,xuzha/elasticsearch,elasticdog/elasticsearch,markwalkom/elasticsearch,jimczi/elasticsearch,mikemccand/elasticsearch,JackyMai/elasticsearch,episerver/elasticsearch,gmarz/elasticsearch,tebriel/elasticsearch,njlawton/elasticsearch,palecur/elasticsearch,nazarewk/elasticsearch,ThiagoGarciaAlves/elasticsearch,gingerwizard/elasticsearch,nilabhsagar/elasticsearch,markharwood/elasticsearch,i-am-Nathan/elasticsearch,uschindler/elasticsearch,obourgain/elasticsearch,nazarewk/elasticsearch,brandonkearby/elasticsearch,jimczi/elasticsearch,nazarewk/elasticsearch,scorpionvicky/elasticsearch,naveenhooda2000/elasticsearch,nomoa/elasticsearch,markwalkom/elasticsearch,awislowski/elasticsearch,coding0011/elasticsearch,xuzha/elasticsearch,markharwood/elasticsearch,sneivandt/elasticsearch,maddin2016/elasticsearch,palecur/elasticsearch,artnowo/elasticsearch,camilojd/elasticsearch,uschindler/elasticsearch,mmaracic/elasticsearch,davidvgalbraith/elasticsearch,gmarz/elasticsearch,ZTE-PaaS/elasticsearch,MaineC/elasticsearch,spiegela/elasticsearch,fforbeck/elasticsearch,liweinan0423/elasticsearch,myelin/elasticsearch,masaruh/elasticsearch,ZTE-PaaS/elasticsearch,uschindler/elasticsearch,bawse/elasticsearch,MaineC/elasticsearch,nknize/elasticsearch,markharwood/elasticsearch,shreejay/elasticsearch,jbertouch/elasticsearch,trangvh/elasticsearch,rajanm/elasticsearch,davidvgalbraith/elasticsearch,liweinan0423/elasticsearch,ESamir/elasticsearch,nezirus/elasticsearch,geidies/elasticsearch,LeoYao/elasticsearch,mapr/elasticsearch,elasticdog/elasticsearch,markharwood/elasticsearch,LewayneNaidoo/elasticsearch,umeshdangat/elasticsearch,geidies/elasticsearch,Helen-Zhao/elasticsearch,girirajsharma/elasticsearch,ZTE-PaaS/elasticsearch,myelin/elasticsearch,clintongormley/elasticsearch,robin13/elasticsearch,dpursehouse/elasticsearch,mortonsykes/elasticsearch,uschindler/elasticsearch,tebriel/elasticsearch,JervyShi/elasticsearch,maddin2016/elasticsearch,wenpos/elasticsearch,girirajsharma/elasticsearch,wangtuo/elasticsearch,umeshdangat/elasticsearch,robin13/elasticsearch,ThiagoGarciaAlves/elasticsearch,JSCooke/elasticsearch,episerver/elasticsearch,wenpos/elasticsearch,elasticdog/elasticsearch,naveenhooda2000/elasticsearch,brandonkearby/elasticsearch,fforbeck/elasticsearch,dpursehouse/elasticsearch,GlenRSmith/elasticsearch,gfyoung/elasticsearch,wuranbo/elasticsearch,StefanGor/elasticsearch,dpursehouse/elasticsearch,alexshadow007/elasticsearch,jprante/elasticsearch,strapdata/elassandra5-rc,fred84/elasticsearch,markharwood/elasticsearch,vroyer/elassandra,henakamaMSFT/elasticsearch,bawse/elasticsearch,dongjoon-hyun/elasticsearch,shreejay/elasticsearch,jchampion/elasticsearch,palecur/elasticsearch,glefloch/elasticsearch,markwalkom/elasticsearch,sreeramjayan/elasticsearch,fernandozhu/elasticsearch,camilojd/elasticsearch,qwerty4030/elasticsearch,sreeramjayan/elasticsearch,sneivandt/elasticsearch,mmaracic/elasticsearch,wuranbo/elasticsearch,ThiagoGarciaAlves/elasticsearch,i-am-Nathan/elasticsearch,zkidkid/elasticsearch,kalimatas/elasticsearch,glefloch/elasticsearch,naveenhooda2000/elasticsearch,C-Bish/elasticsearch,ricardocerq/elasticsearch,nezirus/elasticsearch,yynil/elasticsearch,JervyShi/elasticsearch,spiegela/elasticsearch,Shepard1212/elasticsearch,nazarewk/elasticsearch,strapdata/elassandra,C-Bish/elasticsearch,glefloch/elasticsearch,ricardocerq/elasticsearch,mohit/elasticsearch,C-Bish/elasticsearch,tebriel/elasticsearch,scottsom/elasticsearch,fforbeck/elasticsearch,shreejay/elasticsearch,clintongormley/elasticsearch,fernandozhu/elasticsearch,jbertouch/elasticsearch,fernandozhu/elasticsearch,henakamaMSFT/elasticsearch,clintongormley/elasticsearch,fred84/elasticsearch,LeoYao/elasticsearch,kalimatas/elasticsearch,rlugojr/elasticsearch,winstonewert/elasticsearch,StefanGor/elasticsearch,diendt/elasticsearch,ZTE-PaaS/elasticsearch,JackyMai/elasticsearch,MisterAndersen/elasticsearch,JSCooke/elasticsearch,GlenRSmith/elasticsearch,pozhidaevak/elasticsearch,bawse/elasticsearch,s1monw/elasticsearch,palecur/elasticsearch,tebriel/elasticsearch,camilojd/elasticsearch,qwerty4030/elasticsearch,brandonkearby/elasticsearch,lks21c/elasticsearch,njlawton/elasticsearch,JervyShi/elasticsearch,i-am-Nathan/elasticsearch,mortonsykes/elasticsearch,spiegela/elasticsearch,sreeramjayan/elasticsearch,winstonewert/elasticsearch,episerver/elasticsearch,mohit/elasticsearch,jchampion/elasticsearch,lks21c/elasticsearch,davidvgalbraith/elasticsearch,robin13/elasticsearch,wangtuo/elasticsearch,wangtuo/elasticsearch,LewayneNaidoo/elasticsearch,henakamaMSFT/elasticsearch,gmarz/elasticsearch,vroyer/elasticassandra,ricardocerq/elasticsearch,zkidkid/elasticsearch,glefloch/elasticsearch,StefanGor/elasticsearch,s1monw/elasticsearch,lks21c/elasticsearch,dongjoon-hyun/elasticsearch,winstonewert/elasticsearch,mapr/elasticsearch,MisterAndersen/elasticsearch,mohit/elasticsearch,JSCooke/elasticsearch,JSCooke/elasticsearch,clintongormley/elasticsearch,rlugojr/elasticsearch,mikemccand/elasticsearch,zkidkid/elasticsearch,JervyShi/elasticsearch,ESamir/elasticsearch,rlugojr/elasticsearch,artnowo/elasticsearch,coding0011/elasticsearch,scorpionvicky/elasticsearch,LeoYao/elasticsearch,liweinan0423/elasticsearch,awislowski/elasticsearch,gfyoung/elasticsearch,diendt/elasticsearch,myelin/elasticsearch,alexshadow007/elasticsearch,rajanm/elasticsearch,mikemccand/elasticsearch,umeshdangat/elasticsearch,a2lin/elasticsearch,nknize/elasticsearch,lks21c/elasticsearch,pozhidaevak/elasticsearch,bawse/elasticsearch,robin13/elasticsearch,nezirus/elasticsearch,mjason3/elasticsearch,kalimatas/elasticsearch,a2lin/elasticsearch,awislowski/elasticsearch,scorpionvicky/elasticsearch,diendt/elasticsearch,mjason3/elasticsearch,wuranbo/elasticsearch,trangvh/elasticsearch,nknize/elasticsearch,sneivandt/elasticsearch,GlenRSmith/elasticsearch,JervyShi/elasticsearch,strapdata/elassandra,mmaracic/elasticsearch,gmarz/elasticsearch,girirajsharma/elasticsearch,trangvh/elasticsearch,artnowo/elasticsearch,Stacey-Gammon/elasticsearch,girirajsharma/elasticsearch,nknize/elasticsearch,fred84/elasticsearch,wuranbo/elasticsearch,nilabhsagar/elasticsearch,nomoa/elasticsearch,ThiagoGarciaAlves/elasticsearch,ThiagoGarciaAlves/elasticsearch,awislowski/elasticsearch,s1monw/elasticsearch,davidvgalbraith/elasticsearch,yynil/elasticsearch,uschindler/elasticsearch,Helen-Zhao/elasticsearch,mohit/elasticsearch,mapr/elasticsearch,Helen-Zhao/elasticsearch,cwurm/elasticsearch,yynil/elasticsearch,myelin/elasticsearch,winstonewert/elasticsearch,lks21c/elasticsearch,avikurapati/elasticsearch,trangvh/elasticsearch,obourgain/elasticsearch,maddin2016/elasticsearch,markwalkom/elasticsearch,coding0011/elasticsearch,henakamaMSFT/elasticsearch,jbertouch/elasticsearch,artnowo/elasticsearch,ZTE-PaaS/elasticsearch,i-am-Nathan/elasticsearch,gingerwizard/elasticsearch,diendt/elasticsearch,HonzaKral/elasticsearch,strapdata/elassandra5-rc,geidies/elasticsearch,henakamaMSFT/elasticsearch,alexshadow007/elasticsearch,mapr/elasticsearch,yanjunh/elasticsearch,jprante/elasticsearch,yynil/elasticsearch,shreejay/elasticsearch,naveenhooda2000/elasticsearch,Helen-Zhao/elasticsearch,avikurapati/elasticsearch,qwerty4030/elasticsearch,JackyMai/elasticsearch,mikemccand/elasticsearch,mjason3/elasticsearch,jbertouch/elasticsearch,ESamir/elasticsearch,LeoYao/elasticsearch,elasticdog/elasticsearch,masaruh/elasticsearch,jimczi/elasticsearch,wenpos/elasticsearch,palecur/elasticsearch,yanjunh/elasticsearch,gmarz/elasticsearch,s1monw/elasticsearch,mmaracic/elasticsearch,spiegela/elasticsearch,zkidkid/elasticsearch,avikurapati/elasticsearch,jchampion/elasticsearch,liweinan0423/elasticsearch,Shepard1212/elasticsearch,njlawton/elasticsearch,gfyoung/elasticsearch,masaruh/elasticsearch,camilojd/elasticsearch,xuzha/elasticsearch,cwurm/elasticsearch,clintongormley/elasticsearch,zkidkid/elasticsearch,avikurapati/elasticsearch,rajanm/elasticsearch,episerver/elasticsearch,trangvh/elasticsearch,jchampion/elasticsearch,masaruh/elasticsearch,GlenRSmith/elasticsearch,ESamir/elasticsearch,pozhidaevak/elasticsearch,fforbeck/elasticsearch,C-Bish/elasticsearch,LewayneNaidoo/elasticsearch,LeoYao/elasticsearch,alexshadow007/elasticsearch,strapdata/elassandra,JackyMai/elasticsearch,obourgain/elasticsearch,JSCooke/elasticsearch,s1monw/elasticsearch,jchampion/elasticsearch,a2lin/elasticsearch,jimczi/elasticsearch,scorpionvicky/elasticsearch,jprante/elasticsearch,gingerwizard/elasticsearch,yynil/elasticsearch,cwurm/elasticsearch,sreeramjayan/elasticsearch,GlenRSmith/elasticsearch,MisterAndersen/elasticsearch,a2lin/elasticsearch,HonzaKral/elasticsearch,alexshadow007/elasticsearch,camilojd/elasticsearch,geidies/elasticsearch,camilojd/elasticsearch,MisterAndersen/elasticsearch,markharwood/elasticsearch,wenpos/elasticsearch,HonzaKral/elasticsearch,mmaracic/elasticsearch,IanvsPoplicola/elasticsearch,wangtuo/elasticsearch,wenpos/elasticsearch,yynil/elasticsearch,shreejay/elasticsearch,nilabhsagar/elasticsearch,avikurapati/elasticsearch,C-Bish/elasticsearch,umeshdangat/elasticsearch,sneivandt/elasticsearch,ESamir/elasticsearch,qwerty4030/elasticsearch,MaineC/elasticsearch,fred84/elasticsearch,HonzaKral/elasticsearch,strapdata/elassandra5-rc,cwurm/elasticsearch,artnowo/elasticsearch,mapr/elasticsearch,dongjoon-hyun/elasticsearch,JervyShi/elasticsearch,obourgain/elasticsearch,Shepard1212/elasticsearch,clintongormley/elasticsearch,maddin2016/elasticsearch,fernandozhu/elasticsearch,xuzha/elasticsearch,jbertouch/elasticsearch,dongjoon-hyun/elasticsearch,coding0011/elasticsearch,rajanm/elasticsearch,mmaracic/elasticsearch,IanvsPoplicola/elasticsearch,kalimatas/elasticsearch,nilabhsagar/elasticsearch,gfyoung/elasticsearch,diendt/elasticsearch,markwalkom/elasticsearch,maddin2016/elasticsearch,obourgain/elasticsearch,LeoYao/elasticsearch,fred84/elasticsearch,jprante/elasticsearch,strapdata/elassandra,vroyer/elassandra,yanjunh/elasticsearch,pozhidaevak/elasticsearch,ricardocerq/elasticsearch,MaineC/elasticsearch,liweinan0423/elasticsearch,nomoa/elasticsearch,tebriel/elasticsearch,nazarewk/elasticsearch,qwerty4030/elasticsearch,JackyMai/elasticsearch,xuzha/elasticsearch,Stacey-Gammon/elasticsearch,Stacey-Gammon/elasticsearch,gingerwizard/elasticsearch,dpursehouse/elasticsearch,naveenhooda2000/elasticsearch,gingerwizard/elasticsearch,cwurm/elasticsearch,brandonkearby/elasticsearch,brandonkearby/elasticsearch,wuranbo/elasticsearch,mohit/elasticsearch,winstonewert/elasticsearch,sreeramjayan/elasticsearch,mortonsykes/elasticsearch,MisterAndersen/elasticsearch,myelin/elasticsearch,strapdata/elassandra5-rc,Shepard1212/elasticsearch,scottsom/elasticsearch,IanvsPoplicola/elasticsearch,ThiagoGarciaAlves/elasticsearch,girirajsharma/elasticsearch,spiegela/elasticsearch,ricardocerq/elasticsearch,jprante/elasticsearch,strapdata/elassandra,xuzha/elasticsearch,awislowski/elasticsearch,masaruh/elasticsearch,njlawton/elasticsearch,StefanGor/elasticsearch,rajanm/elasticsearch,vroyer/elasticassandra,LeoYao/elasticsearch,vroyer/elasticassandra,coding0011/elasticsearch,Stacey-Gammon/elasticsearch,a2lin/elasticsearch,bawse/elasticsearch