Resync project repositories on secondaries nodes when import finishes

What does this MR do?

Logs a Geo repository updated event to resync project repositories on the secondaries node when a project import finishes. It also invalidates the repositories checksum.

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

No.

Why was this MR needed?

Project imports may not be synced if the repository takes some time to fetch, what can lead to a potential data loss. We also need to invalidate the checksum. Otherwise, we can have stale checksums on the primary node.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • 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
• Conform 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?

#6888 (closed)