KafkaRebalance resource should be checked for deprecated and unsupported fields

[scholzj]

Most of our resources which follow the main reconciliation cycle (Kafka, KafkaConnect, ...) are using the ValidationVisitor to check the resource and report any fields which are deprecated or which are on wrong / unsupported paths as warning into the log (and after #3623 also in resource status). However, this does not seem to apply to the KafkaRebalance which has its own cycle. The KafkaRebalanceAssemblyOperator should be updated to do this as well. While it currently doesn't have any deprecated fields, it can still have users have unsupported fields in the CR etc.