mgr/cephadm/upgrade: match against any repo_digest, not image_id

mgr/cephadm/upgrade: match against any repo_digest, not image_id

The image id can vary across hosts and (most notably) docker vs podman.
Instead, use the repo_digest as an image identifier.

Unfortunately, a single image may have multiple digests, even within the
same registry, so keep a list of the digests for the image we are
upgrading to, and ensure that each container has a digest that matches at
least one of them.

This allows upgrade to proceed in mixed docker+podman clusters.  However,
it does not yet address a cluster with mixed CPU architectures, because
the container image will have different digest(s) for each architecture
build.

Signed-off-by: Sage Weil <sage@newdream.net>