Add Prometheus metrics to track Geo autocorrect numbers

What does this MR do?

Add Prometheus metrics to track the number of repositories that Geo is currently trying to autocorrect.

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

⚠ Needs MR merged first -> https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6759

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• EE specific content should be in the top level /ee folder
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

#5195 (closed)