Merge branch 'ia-refactor-user-created_by' into 'master'

Add created_by relationship to User model

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/156366



Merged-by: Doug Stull <dstull@gitlab.com>
Approved-by: Shabini Rajadas <srajadas@gitlab.com>
Approved-by: Doug Stull <dstull@gitlab.com>
Reviewed-by: Doug Stull <dstull@gitlab.com>
Reviewed-by: Ian Anderson <ianderson@gitlab.com>
Co-authored-by: imand3r <ianderson@gitlab.com>