Resolve "Permissions for project labels and group labels"

What does this MR do?

Give users with group reporter access or higher the permission to edit group labels.

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

I've moved some code around in the policy to save some queries, and added a spec for some previously untested behaviour.

Why was this MR needed?

Project labels can be set by reporters. No reason for group labels to behave differently.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• 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 #33154 (closed).