Pass user instance to Labels::FindOrCreateService or skip_authorization: true
## What does this MR do?
It fixes a bug described in #23694 when `project.owner` was passed to `Labels::FindOrCreateService`. `Labels::FindOrCreateService` expected a user instance and `project.owner` may return a group as well. This MR makes sure that we either pass a user instance or `skip_authorization: true`.
## Are there points in the code the reviewer needs to double check?
- places where we pass `skip_authorization: true`
## Does this MR meet the acceptance criteria?
- Tests
- [x] Added for this feature/bug
- [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)
## What are the relevant issue numbers?
Fixes#23694
See merge request !7093
44cbfeaba8