[Docs] Update aggregations.asciidoc (#29265)
[Docs] Update aggregations.asciidoc (#29265)

Add note about accuracy of some aggregation results.
HonzaKral/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,rajanm/elasticsearch,gfyoung/elasticsearch,scorpionvicky/elasticsearch,gfyoung/elasticsearch,nknize/elasticsearch,coding0011/elasticsearch,robin13/elasticsearch,uschindler/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,gfyoung/elasticsearch,gfyoung/elasticsearch,gingerwizard/elasticsearch,coding0011/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,gingerwizard/elasticsearch,coding0011/elasticsearch,rajanm/elasticsearch,gingerwizard/elasticsearch,rajanm/elasticsearch,HonzaKral/elasticsearch,uschindler/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,gfyoung/elasticsearch,rajanm/elasticsearch,robin13/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,rajanm/elasticsearch,coding0011/elasticsearch,uschindler/elasticsearch,HonzaKral/elasticsearch,scorpionvicky/elasticsearch,rajanm/elasticsearch,scorpionvicky/elasticsearch,scorpionvicky/elasticsearch,gingerwizard/elasticsearch,robin13/elasticsearch,coding0011/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,robin13/elasticsearch,HonzaKral/elasticsearch,scorpionvicky/elasticsearch