Geo: Replicate keep around refs

What does this MR do?

This MR causes Geo to resync repositories when keep around refs are created. These refs are used in MRs, commenting, etc.

What are the relevant issue numbers?

Resolves https://gitlab.com/gitlab-org/gitlab-ee/issues/7245

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?