Document and test storage resizing on the same nodes

[mflendrich]

Issue originally authored by tnozicka as #825

Given StatefulSet don't reconcile storage changes we can't yet easily handle it in the operator seamlessly and we should at least document a manual procedure. Something in the lines of:

• orphan delete the scyllacluster
• orphan delete the statefulsets
• create the scyllacluster with higher storage request
• resize the existing PVC, if the storage class supports it, replace the nodes if it doesn't
• trigger a scyllacuster rollout

[mflendrich]

The scope is to carry the community PR #2243 through completion.