Do we want epochs tied to hubris images to prevent rollback

Currently, hubris versions are semver included in the caboose. We previously had an idea of using (epoch, version) pairs in order to not allow rolling back to a previous epoch when updating. This is useful for security purposes, like if we want to ensure an old vulnerability cannot be re-activated on a given machine.

The question is whether we still want to use epochs, or some other mechanism. If we do use epochs, where do we store them? In the caboose?

Start by reviewing how semver versions are currently included in the caboose and how Hubris images are updated or rolled back. Decide whether epoch/version pairs or another mechanism should prevent rollback to vulnerable older images, and determine where epoch data would be stored if epochs are retained.