Geo: fix removal of repositories from disk on secondary nodes

What does this MR do?

• Implements tests to cover repository removal on secondary nodes
• Fix the regression

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

Check if proposed workaround for the lack of repository_storage metadata in the Hook notification is good enough or not.

I'm using the gitlab_shell reference from the Project to check existence of the repository, is that compatible with current/future gitaly ?

Why was this MR needed?

There was a regression after the introduction of multiple repository storages that got unnoticed because we lacked spec coverage.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• 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 #2701 (closed)