Move scylla config creation into the operator

[ylebi]

Is this a bug report or feature request?

• Feature Request

What should the feature do:
Scylla config should be built in the operator, then represented as a CM/Secret and mounted into the container. Same goes for the args. Currently it is build in a sidecar which has several disadvantages:

• the sidecar has to run exactly the same image as the operator which is impossible to enforce and breaks with rolling tags
• if any remote call fails it cases a restart
• we can't trigger rolling restarts on changes
• wastes live api call, the operator already has caches with data that needs to be substituted
• is build again for every replica, instead of the operator doing it once
• if config building fails we end up with 1 replica down, while the operator would find out sooner and would stop before trying the first replica
• it can't be revisioned
• needs extra RBAC
• it doesn't honor the Three laws of controllers (ownerRefs, adoption, release)
• it needs additional arguments to know e.g. the manager-agent secret location, while the operator already has all of the prerequisites and caches
• we can't prevent a rollout with invalid config