Clarify doc count stats (#56665)
Clarify doc count stats (#56665)

Today we report some statistics in terms of Lucene-level documents, which
differ from Elasticsearch-level documents in a number of ways and include
things like document tombstones which users cannot directly observe. This
commit clarifies the internal nature of these statistics.

Closes #56497
GlenRSmith/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,gingerwizard/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,uschindler/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,scorpionvicky/elasticsearch,nknize/elasticsearch,scorpionvicky/elasticsearch,scorpionvicky/elasticsearch,uschindler/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch