Add Geo Prometheus metrics about the various number of events

Add metrics for:

• Repository created count
• Repository updated count
• Repository deleted count
• Repository renamed count
• Repositories changed count
• LFS object deleted count
• Job artifact deleted count
• Hashed storage migrated count
• Hashed storage attachments count

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

Is the method of using maximum(:id) a good idea. Or do you consider a better way of working around the Geo::PruneEventLogWorker?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [-] Documentation created/updated
• [-] API support added
• Tests added for this feature/bug
• Review
  • [-] Has been reviewed by UX
  • [-] Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• 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-qa manual pipeline job)

What are the relevant issue numbers?

Closes gitlab-org/gitlab-ee#4688.