Not empty `Volume` can't be encrypted

[lukasfrank]

Describe the bug
If a Volume references an image the Volume can't be encrypted.

{"imageId": "505323310729f021ec9e940ba9e345109fb200bcb46730d706ff716ed9603e1", "error": "failed to set encryption header: failed to set encryption format: rbd: ret=-95, Operation not supported"}
github.com/onmetal/cephlet/pkg/controllers.(*ImageReconciler).

Investigation needed to check expected behaviour.

To Reproduce

metadata:
  name: encryption-test
spec:
  image: ghcr.io/onmetal/onmetal-image/gardenlinux:rootfs-dev-20230223
  volumeClassRef:
    name: general-purpose
  encryption:
    secretRef:
      name: encryption-key-secret
  resources:
    storage: 5Gi

[lukasfrank]

Will be implemented in the next ceph release:
https://docs.ceph.com/en/latest/rbd/rbd-encryption/#examples