Iteratively, we've pushed these checks into a number of different
locations, however having a unified, single-location for these checks is
for more sustainable into the future. By moving the existing "web
request" checks into Commits::CreateService, we can remove the existing
checks previously added to the file editor, enable checks on the Commits
REST API (create/update/delete, cherry-pick, revert), and can remove the
:skip_web_ui_code_owner_validations ermergency workaround