Stop operator upgrades when there is an unsupported scylla version

[mflendrich]

Issue originally authored by tnozicka as #653

Is this a bug report or feature request?

• Feature Request

What should the feature do:

• Operator should fail to start (never become ready) when it lists a scylla cluster with an unsupported scylla version. It will stop operator upgrade to prevent managing an unsupported scylla version.
• Operator won't act on ScyllaClusters with unsupported versions, except for updating status and adding degraded condition with UnsupportedVersion reason. (In case a clusted would be recreated / adopted.)

What is use case behind this feature:
Prevent working with unsupported scylla versions that would break, like when it doesn't have seedless support.