mgr/dashboard: query the registry for available images
What versions are available in the registry?
We should make this information available by comparing the version of the currently deployed container images vs the available images on the defined registry.
This PR: https://github.com/ceph/ceph/pull/36280 contains an implementation to query the registry. this PR is no longer needed for cephadm as we can simply upgrade to :latest. Might be something for the dashboard?