[docs] Add missing RUN command from custom docker config
[docs] Add missing RUN command from custom docker config

Fix the `Dockerfile` example in the `Customizing image` third configuration
method by adding the missing RUN instruction.

Originally reported by Shankar Vasudevan (@vshank77).

Relates #21973
rajanm/elasticsearch,bawse/elasticsearch,nknize/elasticsearch,qwerty4030/elasticsearch,Stacey-Gammon/elasticsearch,C-Bish/elasticsearch,bawse/elasticsearch,mjason3/elasticsearch,wenpos/elasticsearch,elasticdog/elasticsearch,maddin2016/elasticsearch,elasticdog/elasticsearch,mohit/elasticsearch,rlugojr/elasticsearch,gingerwizard/elasticsearch,C-Bish/elasticsearch,coding0011/elasticsearch,mohit/elasticsearch,i-am-Nathan/elasticsearch,coding0011/elasticsearch,nilabhsagar/elasticsearch,lks21c/elasticsearch,fred84/elasticsearch,C-Bish/elasticsearch,rajanm/elasticsearch,winstonewert/elasticsearch,winstonewert/elasticsearch,LewayneNaidoo/elasticsearch,wenpos/elasticsearch,jimczi/elasticsearch,rajanm/elasticsearch,gingerwizard/elasticsearch,LeoYao/elasticsearch,StefanGor/elasticsearch,a2lin/elasticsearch,gfyoung/elasticsearch,obourgain/elasticsearch,uschindler/elasticsearch,markwalkom/elasticsearch,LewayneNaidoo/elasticsearch,robin13/elasticsearch,shreejay/elasticsearch,robin13/elasticsearch,rajanm/elasticsearch,mjason3/elasticsearch,s1monw/elasticsearch,geidies/elasticsearch,glefloch/elasticsearch,umeshdangat/elasticsearch,geidies/elasticsearch,nazarewk/elasticsearch,C-Bish/elasticsearch,mjason3/elasticsearch,nazarewk/elasticsearch,JSCooke/elasticsearch,LewayneNaidoo/elasticsearch,GlenRSmith/elasticsearch,LeoYao/elasticsearch,Helen-Zhao/elasticsearch,gingerwizard/elasticsearch,naveenhooda2000/elasticsearch,pozhidaevak/elasticsearch,qwerty4030/elasticsearch,nazarewk/elasticsearch,masaruh/elasticsearch,maddin2016/elasticsearch,StefanGor/elasticsearch,IanvsPoplicola/elasticsearch,nknize/elasticsearch,sneivandt/elasticsearch,fernandozhu/elasticsearch,alexshadow007/elasticsearch,mjason3/elasticsearch,scottsom/elasticsearch,lks21c/elasticsearch,kalimatas/elasticsearch,geidies/elasticsearch,a2lin/elasticsearch,JSCooke/elasticsearch,mikemccand/elasticsearch,markwalkom/elasticsearch,StefanGor/elasticsearch,pozhidaevak/elasticsearch,scorpionvicky/elasticsearch,alexshadow007/elasticsearch,fred84/elasticsearch,winstonewert/elasticsearch,njlawton/elasticsearch,winstonewert/elasticsearch,brandonkearby/elasticsearch,njlawton/elasticsearch,ZTE-PaaS/elasticsearch,winstonewert/elasticsearch,jimczi/elasticsearch,obourgain/elasticsearch,mjason3/elasticsearch,sneivandt/elasticsearch,IanvsPoplicola/elasticsearch,rlugojr/elasticsearch,strapdata/elassandra,markwalkom/elasticsearch,robin13/elasticsearch,Shepard1212/elasticsearch,artnowo/elasticsearch,fernandozhu/elasticsearch,masaruh/elasticsearch,artnowo/elasticsearch,GlenRSmith/elasticsearch,nknize/elasticsearch,artnowo/elasticsearch,kalimatas/elasticsearch,gingerwizard/elasticsearch,ThiagoGarciaAlves/elasticsearch,umeshdangat/elasticsearch,mortonsykes/elasticsearch,IanvsPoplicola/elasticsearch,elasticdog/elasticsearch,lks21c/elasticsearch,Stacey-Gammon/elasticsearch,njlawton/elasticsearch,i-am-Nathan/elasticsearch,MisterAndersen/elasticsearch,glefloch/elasticsearch,fernandozhu/elasticsearch,uschindler/elasticsearch,gfyoung/elasticsearch,JackyMai/elasticsearch,Stacey-Gammon/elasticsearch,naveenhooda2000/elasticsearch,uschindler/elasticsearch,gfyoung/elasticsearch,mikemccand/elasticsearch,StefanGor/elasticsearch,vroyer/elasticassandra,uschindler/elasticsearch,i-am-Nathan/elasticsearch,a2lin/elasticsearch,sneivandt/elasticsearch,elasticdog/elasticsearch,nilabhsagar/elasticsearch,nezirus/elasticsearch,gfyoung/elasticsearch,obourgain/elasticsearch,a2lin/elasticsearch,elasticdog/elasticsearch,mikemccand/elasticsearch,MisterAndersen/elasticsearch,strapdata/elassandra,mikemccand/elasticsearch,strapdata/elassandra,i-am-Nathan/elasticsearch,geidies/elasticsearch,qwerty4030/elasticsearch,kalimatas/elasticsearch,glefloch/elasticsearch,vroyer/elassandra,jprante/elasticsearch,MisterAndersen/elasticsearch,ThiagoGarciaAlves/elasticsearch,s1monw/elasticsearch,fred84/elasticsearch,alexshadow007/elasticsearch,LeoYao/elasticsearch,scorpionvicky/elasticsearch,alexshadow007/elasticsearch,IanvsPoplicola/elasticsearch,nilabhsagar/elasticsearch,naveenhooda2000/elasticsearch,StefanGor/elasticsearch,rlugojr/elasticsearch,gingerwizard/elasticsearch,HonzaKral/elasticsearch,qwerty4030/elasticsearch,shreejay/elasticsearch,JackyMai/elasticsearch,maddin2016/elasticsearch,njlawton/elasticsearch,fred84/elasticsearch,ZTE-PaaS/elasticsearch,Helen-Zhao/elasticsearch,ThiagoGarciaAlves/elasticsearch,brandonkearby/elasticsearch,wangtuo/elasticsearch,mohit/elasticsearch,ThiagoGarciaAlves/elasticsearch,GlenRSmith/elasticsearch,fernandozhu/elasticsearch,HonzaKral/elasticsearch,gingerwizard/elasticsearch,Helen-Zhao/elasticsearch,robin13/elasticsearch,nezirus/elasticsearch,uschindler/elasticsearch,mortonsykes/elasticsearch,masaruh/elasticsearch,GlenRSmith/elasticsearch,rajanm/elasticsearch,fred84/elasticsearch,Helen-Zhao/elasticsearch,jimczi/elasticsearch,naveenhooda2000/elasticsearch,scottsom/elasticsearch,wenpos/elasticsearch,markwalkom/elasticsearch,wangtuo/elasticsearch,LeoYao/elasticsearch,wenpos/elasticsearch,vroyer/elassandra,obourgain/elasticsearch,scottsom/elasticsearch,bawse/elasticsearch,jprante/elasticsearch,Shepard1212/elasticsearch,scorpionvicky/elasticsearch,obourgain/elasticsearch,LeoYao/elasticsearch,Shepard1212/elasticsearch,mohit/elasticsearch,coding0011/elasticsearch,fernandozhu/elasticsearch,s1monw/elasticsearch,JSCooke/elasticsearch,jprante/elasticsearch,nezirus/elasticsearch,bawse/elasticsearch,ZTE-PaaS/elasticsearch,brandonkearby/elasticsearch,nezirus/elasticsearch,maddin2016/elasticsearch,pozhidaevak/elasticsearch,naveenhooda2000/elasticsearch,wangtuo/elasticsearch,brandonkearby/elasticsearch,s1monw/elasticsearch,mortonsykes/elasticsearch,glefloch/elasticsearch,jimczi/elasticsearch,rlugojr/elasticsearch,JSCooke/elasticsearch,ZTE-PaaS/elasticsearch,umeshdangat/elasticsearch,HonzaKral/elasticsearch,masaruh/elasticsearch,sneivandt/elasticsearch,masaruh/elasticsearch,JackyMai/elasticsearch,brandonkearby/elasticsearch,rajanm/elasticsearch,LeoYao/elasticsearch,ThiagoGarciaAlves/elasticsearch,C-Bish/elasticsearch,wangtuo/elasticsearch,Shepard1212/elasticsearch,umeshdangat/elasticsearch,LeoYao/elasticsearch,a2lin/elasticsearch,nilabhsagar/elasticsearch,mortonsykes/elasticsearch,wenpos/elasticsearch,pozhidaevak/elasticsearch,nilabhsagar/elasticsearch,artnowo/elasticsearch,scorpionvicky/elasticsearch,alexshadow007/elasticsearch,geidies/elasticsearch,artnowo/elasticsearch,gingerwizard/elasticsearch,jprante/elasticsearch,LewayneNaidoo/elasticsearch,kalimatas/elasticsearch,vroyer/elassandra,strapdata/elassandra,shreejay/elasticsearch,GlenRSmith/elasticsearch,nezirus/elasticsearch,nknize/elasticsearch,JackyMai/elasticsearch,markwalkom/elasticsearch,bawse/elasticsearch,mortonsykes/elasticsearch,nazarewk/elasticsearch,JSCooke/elasticsearch,maddin2016/elasticsearch,coding0011/elasticsearch,pozhidaevak/elasticsearch,ThiagoGarciaAlves/elasticsearch,s1monw/elasticsearch,lks21c/elasticsearch,vroyer/elasticassandra,LewayneNaidoo/elasticsearch,qwerty4030/elasticsearch,Stacey-Gammon/elasticsearch,sneivandt/elasticsearch,Helen-Zhao/elasticsearch,Shepard1212/elasticsearch,rlugojr/elasticsearch,robin13/elasticsearch,nknize/elasticsearch,shreejay/elasticsearch,MisterAndersen/elasticsearch,IanvsPoplicola/elasticsearch,HonzaKral/elasticsearch,nazarewk/elasticsearch,markwalkom/elasticsearch,umeshdangat/elasticsearch,vroyer/elasticassandra,gfyoung/elasticsearch,geidies/elasticsearch,kalimatas/elasticsearch,glefloch/elasticsearch,MisterAndersen/elasticsearch,lks21c/elasticsearch,coding0011/elasticsearch,strapdata/elassandra,Stacey-Gammon/elasticsearch,scorpionvicky/elasticsearch,JackyMai/elasticsearch,wangtuo/elasticsearch,scottsom/elasticsearch,jprante/elasticsearch,ZTE-PaaS/elasticsearch,shreejay/elasticsearch,mikemccand/elasticsearch,i-am-Nathan/elasticsearch,scottsom/elasticsearch,njlawton/elasticsearch,jimczi/elasticsearch,mohit/elasticsearch