Document and/or improve uninstallation

Coming out of https://bugzilla.redhat.com/show_bug.cgi?id=2113831 and the associated thread, we need a better story around uninstalling hive. At the very least, we need to document the accepted procedure. Based on an e2e test it's reasonably complex, involving deleting a lot of the resources laid down by hive-operator.

It may also be possible to have hive-operator itself do the uninstallation when it is deleted. (When what is deleted? The pod? Then we'll "clean up" every time the deployment cycles e.g. for upgrades. Which actually might be the right thing. The deployment? Then we'll have to have the pod detect that the deployment is being deleted, which is weird.) Investigation required.