Merge branch 'cz-advanced-search-concurrency-doc' into 'master'

Doc update for advanced search code indexing concurrency setting

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/143448



Merged-by: Jon Glassman <jglassman@gitlab.com>
Approved-by: Jon Glassman <jglassman@gitlab.com>
Approved-by: Dmitry Gruzd <dgruzd@gitlab.com>
Co-authored-by: Changzheng Liu <cliu@gitlab.com>