juju-blobstore-cleanup should remove resources that are part of live models but no longer referenced

[John A Meinel]

One limitation of the juju-blobstore-cleanup was that we took a safe approach and only delete content that we *know* is not referenced. (It belongs to a model that no longer exists.)

However, there are still things that we could be fairly sure are no longer needed. (Old versions of charms that *were* used, but for historical reasons didn't get cleaned up.)

We need to be careful about whether they are actually referenced, but as long as we track all places where we call ManagedStorage should give us confidence that we are handling them. (juju-list-blobstore currently doesn't do backups and images, but should otherwise be complete.)

[Canonical Juju QA Bot (juju-qa-bot)]

This bug has not been updated in 2 years, so we're marking it Low importance. If you believe this is incorrect, please update the importance.