Cluster allocation explain API documentation (#22436)
Cluster allocation explain API documentation (#22436)

This commit updates the cluster allocation explain API documentation to
explain the new request parameters and response formats, and gives
examples of the explain API responses under various scenarios.

winstonewert/elasticsearch,strapdata/elassandra,mikemccand/elasticsearch,mohit/elasticsearch,jprante/elasticsearch,ZTE-PaaS/elasticsearch,uschindler/elasticsearch,lks21c/elasticsearch,jimczi/elasticsearch,GlenRSmith/elasticsearch,IanvsPoplicola/elasticsearch,HonzaKral/elasticsearch,jimczi/elasticsearch,vroyer/elasticassandra,njlawton/elasticsearch,markwalkom/elasticsearch,JackyMai/elasticsearch,brandonkearby/elasticsearch,nazarewk/elasticsearch,qwerty4030/elasticsearch,scottsom/elasticsearch,maddin2016/elasticsearch,nezirus/elasticsearch,brandonkearby/elasticsearch,obourgain/elasticsearch,mikemccand/elasticsearch,gfyoung/elasticsearch,maddin2016/elasticsearch,LewayneNaidoo/elasticsearch,alexshadow007/elasticsearch,geidies/elasticsearch,Stacey-Gammon/elasticsearch,naveenhooda2000/elasticsearch,coding0011/elasticsearch,i-am-Nathan/elasticsearch,glefloch/elasticsearch,naveenhooda2000/elasticsearch,uschindler/elasticsearch,kalimatas/elasticsearch,vroyer/elassandra,pozhidaevak/elasticsearch,MisterAndersen/elasticsearch,robin13/elasticsearch,MisterAndersen/elasticsearch,MisterAndersen/elasticsearch,HonzaKral/elasticsearch,s1monw/elasticsearch,njlawton/elasticsearch,mortonsykes/elasticsearch,artnowo/elasticsearch,bawse/elasticsearch,nknize/elasticsearch,lks21c/elasticsearch,mortonsykes/elasticsearch,mikemccand/elasticsearch,alexshadow007/elasticsearch,kalimatas/elasticsearch,strapdata/elassandra,a2lin/elasticsearch,LewayneNaidoo/elasticsearch,nknize/elasticsearch,gfyoung/elasticsearch,qwerty4030/elasticsearch,bawse/elasticsearch,Stacey-Gammon/elasticsearch,gingerwizard/elasticsearch,JackyMai/elasticsearch,JSCooke/elasticsearch,geidies/elasticsearch,ThiagoGarciaAlves/elasticsearch,rajanm/elasticsearch,MisterAndersen/elasticsearch,JSCooke/elasticsearch,HonzaKral/elasticsearch,qwerty4030/elasticsearch,jprante/elasticsearch,Shepard1212/elasticsearch,artnowo/elasticsearch,jimczi/elasticsearch,fernandozhu/elasticsearch,coding0011/elasticsearch,HonzaKral/elasticsearch,StefanGor/elasticsearch,shreejay/elasticsearch,Helen-Zhao/elasticsearch,glefloch/elasticsearch,s1monw/elasticsearch,Helen-Zhao/elasticsearch,coding0011/elasticsearch,umeshdangat/elasticsearch,ThiagoGarciaAlves/elasticsearch,umeshdangat/elasticsearch,geidies/elasticsearch,elasticdog/elasticsearch,maddin2016/elasticsearch,mikemccand/elasticsearch,jprante/elasticsearch,nilabhsagar/elasticsearch,scorpionvicky/elasticsearch,robin13/elasticsearch,pozhidaevak/elasticsearch,s1monw/elasticsearch,wangtuo/elasticsearch,nknize/elasticsearch,vroyer/elasticassandra,ZTE-PaaS/elasticsearch,ThiagoGarciaAlves/elasticsearch,pozhidaevak/elasticsearch,geidies/elasticsearch,markwalkom/elasticsearch,C-Bish/elasticsearch,scottsom/elasticsearch,ThiagoGarciaAlves/elasticsearch,sneivandt/elasticsearch,gingerwizard/elasticsearch,sneivandt/elasticsearch,markwalkom/elasticsearch,Shepard1212/elasticsearch,shreejay/elasticsearch,njlawton/elasticsearch,scorpionvicky/elasticsearch,s1monw/elasticsearch,rajanm/elasticsearch,StefanGor/elasticsearch,LewayneNaidoo/elasticsearch,gingerwizard/elasticsearch,pozhidaevak/elasticsearch,uschindler/elasticsearch,mortonsykes/elasticsearch,fred84/elasticsearch,fred84/elasticsearch,alexshadow007/elasticsearch,alexshadow007/elasticsearch,a2lin/elasticsearch,obourgain/elasticsearch,mohit/elasticsearch,Shepard1212/elasticsearch,gfyoung/elasticsearch,rlugojr/elasticsearch,artnowo/elasticsearch,GlenRSmith/elasticsearch,Helen-Zhao/elasticsearch,rajanm/elasticsearch,gingerwizard/elasticsearch,brandonkearby/elasticsearch,nknize/elasticsearch,gingerwizard/elasticsearch,JackyMai/elasticsearch,LeoYao/elasticsearch,shreejay/elasticsearch,naveenhooda2000/elasticsearch,shreejay/elasticsearch,strapdata/elassandra,nilabhsagar/elasticsearch,jprante/elasticsearch,winstonewert/elasticsearch,fred84/elasticsearch,i-am-Nathan/elasticsearch,uschindler/elasticsearch,GlenRSmith/elasticsearch,rlugojr/elasticsearch,s1monw/elasticsearch,mortonsykes/elasticsearch,fred84/elasticsearch,wangtuo/elasticsearch,umeshdangat/elasticsearch,shreejay/elasticsearch,ThiagoGarciaAlves/elasticsearch,wenpos/elasticsearch,strapdata/elassandra,mjason3/elasticsearch,i-am-Nathan/elasticsearch,Helen-Zhao/elasticsearch,mohit/elasticsearch,strapdata/elassandra,naveenhooda2000/elasticsearch,artnowo/elasticsearch,i-am-Nathan/elasticsearch,LewayneNaidoo/elasticsearch,pozhidaevak/elasticsearch,coding0011/elasticsearch,rlugojr/elasticsearch,rajanm/elasticsearch,obourgain/elasticsearch,JackyMai/elasticsearch,mjason3/elasticsearch,wangtuo/elasticsearch,Stacey-Gammon/elasticsearch,obourgain/elasticsearch,LeoYao/elasticsearch,a2lin/elasticsearch,naveenhooda2000/elasticsearch,GlenRSmith/elasticsearch,rlugojr/elasticsearch,winstonewert/elasticsearch,StefanGor/elasticsearch,scottsom/elasticsearch,njlawton/elasticsearch,coding0011/elasticsearch,LeoYao/elasticsearch,mikemccand/elasticsearch,elasticdog/elasticsearch,nilabhsagar/elasticsearch,vroyer/elasticassandra,jimczi/elasticsearch,wangtuo/elasticsearch,wenpos/elasticsearch,kalimatas/elasticsearch,i-am-Nathan/elasticsearch,masaruh/elasticsearch,GlenRSmith/elasticsearch,JSCooke/elasticsearch,LeoYao/elasticsearch,C-Bish/elasticsearch,sneivandt/elasticsearch,glefloch/elasticsearch,gingerwizard/elasticsearch,ThiagoGarciaAlves/elasticsearch,brandonkearby/elasticsearch,umeshdangat/elasticsearch,elasticdog/elasticsearch,mjason3/elasticsearch,C-Bish/elasticsearch,kalimatas/elasticsearch,alexshadow007/elasticsearch,bawse/elasticsearch,glefloch/elasticsearch,wenpos/elasticsearch,LewayneNaidoo/elasticsearch,markwalkom/elasticsearch,masaruh/elasticsearch,sneivandt/elasticsearch,JSCooke/elasticsearch,scorpionvicky/elasticsearch,vroyer/elassandra,qwerty4030/elasticsearch,lks21c/elasticsearch,sneivandt/elasticsearch,ZTE-PaaS/elasticsearch,jimczi/elasticsearch,C-Bish/elasticsearch,Shepard1212/elasticsearch,IanvsPoplicola/elasticsearch,IanvsPoplicola/elasticsearch,robin13/elasticsearch,elasticdog/elasticsearch,winstonewert/elasticsearch,StefanGor/elasticsearch,uschindler/elasticsearch,mortonsykes/elasticsearch,robin13/elasticsearch,gfyoung/elasticsearch,masaruh/elasticsearch,fernandozhu/elasticsearch,wangtuo/elasticsearch,brandonkearby/elasticsearch,bawse/elasticsearch,maddin2016/elasticsearch,nilabhsagar/elasticsearch,ZTE-PaaS/elasticsearch,Shepard1212/elasticsearch,wenpos/elasticsearch,fernandozhu/elasticsearch,LeoYao/elasticsearch,maddin2016/elasticsearch,Stacey-Gammon/elasticsearch,mohit/elasticsearch,qwerty4030/elasticsearch,masaruh/elasticsearch,vroyer/elassandra,geidies/elasticsearch,rajanm/elasticsearch,Stacey-Gammon/elasticsearch,fernandozhu/elasticsearch,nezirus/elasticsearch,mohit/elasticsearch,nknize/elasticsearch,a2lin/elasticsearch,nezirus/elasticsearch,nazarewk/elasticsearch,LeoYao/elasticsearch,mjason3/elasticsearch,lks21c/elasticsearch,nazarewk/elasticsearch,LeoYao/elasticsearch,StefanGor/elasticsearch,gfyoung/elasticsearch,winstonewert/elasticsearch,IanvsPoplicola/elasticsearch,markwalkom/elasticsearch,elasticdog/elasticsearch,scorpionvicky/elasticsearch,IanvsPoplicola/elasticsearch,ZTE-PaaS/elasticsearch,obourgain/elasticsearch,nazarewk/elasticsearch,nezirus/elasticsearch,lks21c/elasticsearch,JSCooke/elasticsearch,jprante/elasticsearch,geidies/elasticsearch,umeshdangat/elasticsearch,kalimatas/elasticsearch,scorpionvicky/elasticsearch,njlawton/elasticsearch,nazarewk/elasticsearch,a2lin/elasticsearch,bawse/elasticsearch,scottsom/elasticsearch,JackyMai/elasticsearch,gingerwizard/elasticsearch,artnowo/elasticsearch,rajanm/elasticsearch,nilabhsagar/elasticsearch,mjason3/elasticsearch,wenpos/elasticsearch,glefloch/elasticsearch,C-Bish/elasticsearch,fred84/elasticsearch,rlugojr/elasticsearch,fernandozhu/elasticsearch,markwalkom/elasticsearch,robin13/elasticsearch,masaruh/elasticsearch,nezirus/elasticsearch,Helen-Zhao/elasticsearch,scottsom/elasticsearch,MisterAndersen/elasticsearch