Make user/author use project.creator in most factories

What does this MR do?

This makes the author/user association of several factory objects default to their project's creator.

Are there points in the code the reviewer needs to double check?

In somes cases, the author now needs to be explicitly created as the test doesn't expect it to be the project's creator.

Why was this MR needed?

To create less DB user records, with the goal to speed-up our pipelines a bit.

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Backend
• 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?

Closes #36009 (closed)