Merge branch 'intro-searching-in-gitlab' into 'master'

Add intro to Searching in GitLab

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/149866



Merged-by: Terri Chu <tchu@gitlab.com>
Approved-by: Dmitry Gruzd <dgruzd@gitlab.com>
Approved-by: Terri Chu <tchu@gitlab.com>
Reviewed-by: Terri Chu <tchu@gitlab.com>
Co-authored-by: Ashraf Khamis <akhamis@gitlab.com>