DBODClass support

Create a pool of DBoD instances.

Implement QoS support on the DBoD operator inspired by StorageClass. Don't change existing logic that creates a DB on the specified DBoD instance, but allow for picking instances from a pool of instances of the same quality class:

• new CRD: DBoDClass, with a list of DBoD hosts that provide that quality level, in admin NS
• new field DBODRegistration.spec.DBODClass that gives the class name
• logic: random assignment at first
• DBODRegistration -> DBODClass -> random DBOD instance -> DBOD admin credentials -> provision DB