Draft: Add unlock_artifacts API endpoint

What does this MR do?

This adds the unlock_artifacts API endpoint inside the pipelines/ namespace, the purpose of this API endpoint is to set the locked column of all the pipelines (in a given project) to "unlocked". This will allow artifact, when they expire, to be deleted and result in reduced storage of artifacts.

Resolves #292394 (closed)

Screenshots (strongly suggested)

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