WIP: Forbid repository access when in lock

This is proof of concept

What does this MR do?

Makes sure that we are not accessing any repository data during lock, because accessing FS is catastrophic :)

Why was this MR needed?

To make sure that we do not lock for longer than needed.

Screenshots (if relevant)

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?

To fix things like this: https://gitlab.com/gitlab-org/gitlab-ce/issues/23503