[Backport 2.x] Backport INDEX_SEARCHER threadpool changes to support task resource tracking for concurrent segment search

[jed326]

#7502 has been merged into main but we need to backport this to 2.x still so that we are not missing the resource tracking features whenever concurrent search is GA in 2.x.

ThreadpoolType.RESIZABLE does not exist in 2.x so we will need to use the existing auto queue threadpool type instead.

Closed backport PR: #7613

[jed326]

Backport PR #7765 is merged