Indicate upgradable condition on ScyllaOperatorConfig

[mflendrich]

Issue originally authored by tnozicka as #833

Is this a bug report or feature request?

• Feature Request

What should the feature do:
ScyllaOpearatorConfig should indicate whether all sidecars have been updated to their desired spec and if it's safe to upgrade the operator. The condition is also useful for automatic upgrades, like with OLM.
(We should also indicate how many clusters use which versions of scylla and the operator so we need the data anyways.)

What is use case behind this feature:
We support only N-1 compatibility for the operator. When jumping multiple versions user needs to know if all cluster have been reconciled and have the new sidecar. If the operator is upgraded before that, there will be N-2 skew.