Fix import behavior and specs on conflicting namespaces

What does this MR do?

Fix import behavior and specs on conflicting namespaces

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

Well, since the spec examples didn't correctly describe the behavior, make sure that the new behavior is the actually intended one.

Why was this MR needed?

The specs specify that in the case of conflicting namespaces on an import, if the existing namespace is not owned by current_user, the project will be created in that user's namespace instead. This change correctly implements that behvaior and fixes the spec examples to test it properly.

Screenshots

Now, as specified by the specs, if you attempt to import into a namespace you don't own, the project will be imported into your personal namespace instead.

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• 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?

Closes #23932 (moved)