mgr/cephadm/upgrade.py: normalize_image_digest has a hard coded constant to docker.io
I mean it's clearly wrong as this depends on the search-regiestries setting of the hosts and is not a constant.
Can we drop this "normalizing" step altogether?
Still, we have to avoid creating a regression to https://github.com/ceph/ceph/pull/40577
This is also an issue in the binary https://github.com/ceph/ceph/blob/master/src/cephadm/cephadm#L4011.
That one actually causes issues when using a local repo and having use_repo_digest on. Since localhost:port/whatever has no "." in it it isn't considered a full name so when ever cephadm tries to pull the container digests it returns something like docker.io/localhost:port/whatever/SHA which it can't pull.