Merge branch '434219-add-allow-anonymous-searches-ff' into 'master'

Add allow_anonymous_searches feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/138975



Merged-by: Terri Chu <tchu@gitlab.com>
Approved-by: Ravi Kumar <rkumar@gitlab.com>
Approved-by: Terri Chu <tchu@gitlab.com>
Reviewed-by: Terri Chu <tchu@gitlab.com>
Co-authored-by: Dmitry Gruzd <dgruzd@gitlab.com>