Rename Elasticsearch to Advanced Global Search

As far as I know, we already call Elasticsearch 'Global Search' here and there, but in the documentation we don't. We should call it what it is, not by the underlying tech.

Proposal

Rename all instances where we're referring to the feature 'Elasticsearch' to 'Global Search'.

Here and there we should still refer to the tech, of course, so this should happen with a precision instrument.

cc @seanpackham @axil @marcia @victorwu @vsizov