Comment 4 for bug 1996809

With regard to setting the default storage-class for the cluster, George makes a great point that the control-plane charm already has a config option called 'default-storage'

Currently this setting only applies when related to ceph-mon to select cephfs, ceph-ext4, or ceph-xfs. The default is "auto" which just sets ceph-xfs as the default if ceph is enabled.

I'd propose a refactor of the logic behind `default-storage` config option. "auto" seems farfetched -- so we should probably just let it continue to mean "ceph-xfs" since it really can't mean anything else at this point[1]

[1]: https://github.com/charmed-kubernetes/cdk-addons/blob/651070382303a86c7f09cfb1048140c4a6c9b386/cdk-addons/apply#L121-L122

> on.config.changed.default-storage
> on.update-status
   list all storage-classes in the cluster
   remove default annotation from all storage-classes in the cluster
   case of default-storage
   if "auto":
     -- add annotation to storage-class/ceph-xfs if it exists in the cluster
   else:
     -- add annotation to storage-class/{default-storage} if it exists in the cluster

I don't care for the poll on update-status, sadly, I know of no way for the charm to watch for external annotation changes to all the storage classes in the cluster and to react on that change.