Pass user instance to Labels::FindOrCreateService or skip_authorization: true

What does this MR do?

It fixes a bug described in #23694 (closed) 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
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Fixes #23694 (closed)