Support `kubectl scale` and the /scale subresource

[mflendrich]

Issue originally authored by tnozicka as #497

Is this a bug report or feature request?

• Feature Request

What should the feature do:

# kubectl get scyllacluster/basic
NAME    AGE
basic   3m57s

# kubectl scale scyllacluster/basic --replicas=3
Error from server (NotFound): scyllaclusters.scylla.scylladb.com "basic" not found

What is use case behind this feature:

Additional Information:
We need to support the scale subresource.