Handle a CODEOWNERS file in a .github-folder
When a repository has a `.github/CODEOWNERS` file we could mention to the user that they need to move the `CODEOWNERS` file to one of the locations we share with GitHub: the root of the repository, or `docs/`.
We might also try to use the `.github/CODEOWNERS` file, but it's not given that the usernames would be the same on both platforms. Users specified by email would keep working.
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The following discussion from !6916 should be addressed:
- [ ] @reprazent started a [discussion](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6916#note_95473258): (+1 comment)
> Should we also allow `.github/CODEOWNERS` to support people ~movingtogitlab?
>
> cc @jramsay
issue