Add metrics for terraform state version replication

What does this MR do?

This mostly just adds documentation and tests to ensure that the self service metrics are enabled correctly for terraform state version replication

This code puts it behind a feature flag automatically as a part of the self service framework, so no Changelog is included. There will be a changelog as a part of the final merge request that also enables the feature, also there was a database changelog for this work in a prior merge request.

#237927 (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.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team