CRD update process for new version of the Operators

[zaultooz]

Hey Stackable team

I have encountered the issue which seems to a common one regarding CRDs and how to handle the versioning/updates of them.

As helm seems to taken a defensive stance on the matter, I think it would be good to have sections dedicated to logging changes and instruction on, how to update already existing CRDs in your cluster.

The purpose of these docs would be to reduce the risk of a customer not being aware of the procedure there is around CRD and potentially safeguard them against force updating the CRD. Updating the CRDs without the proper procedure could result in objects being wiped as a side effect.