Geo: Add rake task to check DB replication

What does this MR do?

Add rake task which exits 0 if Geo DB replication is working, and exits 1 if not.

This task can be used programmatically to determine whether to run replicate-geo-database on a secondary.

Resolves #245530 (closed)

Related gitlab-orchestrator#200 (closed)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.