Admin - Cleanup repositories using their associated policies task should lazily mark maven metadata for rebuild

Currently as the cleanup task for cleanup policies rebuilds removes Maven assets, maven metadata is rebuilt synchronously.

Rebuilding Maven metadata can be an expensive operation. To improve the completion time of the Cleanup task, the task should avoid rebuilding maven metadata synchronously during the task.

Expected

Make the cleanup task flag maven metadata as "dirty", and then rebuild maven metadata only when it is requested during a build, or by another operation that is meant to explicitly rebuild maven metadata.