Geo: Refactor: Extract verification concern

What does this MR do?

This is a refactor which extracts verification logic to a concern which can be used by both BlobReplicatorStrategy and RepositoryReplicatorStrategy.

This is in preparation for more verification code related to #13981 (closed) and #13839 (closed).

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry => Refactor only
• [-] 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.