Default enable FF search_index_all_projects

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/145300



Merged-by: Siddharth Dungarwal <sdungarwal@gitlab.com>
Approved-by: Ashraf Khamis <akhamis@gitlab.com>
Approved-by: Arpit Gogia <12347103-arpitgogia@users.noreply.gitlab.com>
Approved-by: Ross Byrne <robyrne@gitlab.com>
Approved-by: Phil Hughes <me@iamphill.com>
Approved-by: Siddharth Dungarwal <sdungarwal@gitlab.com>
Reviewed-by: Terri Chu <tchu@gitlab.com>
Co-authored-by: Ashraf Khamis <akhamis@gitlab.com>
Co-authored-by: Terri Chu <tchu@gitlab.com>