`minio` charm does not refresh relations if relation is removed

[ca-scribner]

If minio is related over the object-storage relation to something that does not fulfil the relation contract (for example, it does not send the SDI versions data), it will be stuck like:

minio/0*   waiting   idle   10.1.208.162  9000/TCP,9001/TCP  List of <ops.model.Relation object-storage:0> versions not found for apps: kfp-ui

If we then break the relation (juju remove-relation minio kfp-ui), the charm status remains as seen above. This is probably because we don't observe the relation broken event, or don't account for how the relation-broken event may or may not have the departing application's data in it.

The minio charm does work properly when we re-relate to something that functions properly, or likely on a config-changed event

Note: this issue likely affects other charms as well