rbd: implement CSI-Addons ControllerGetVolumeGroup operation

With the ControllerGetVolumeGroup operation the caller can verify that a
VolumeGroup exists, and validate the volumes that are part of it.

Signed-off-by: Niels de Vos <ndevos@ibm.com>

internal/csi-addons/rbd/identity.go

@@ -120,6 +120,12 @@ func (is *IdentityServer) GetCapabilities(
 						Type: identity.Capability_VolumeGroup_MODIFY_VOLUME_GROUP,
 					},
 				},
+			}, &identity.Capability{
+				Type: &identity.Capability_VolumeGroup_{
+					VolumeGroup: &identity.Capability_VolumeGroup{
+						Type: identity.Capability_VolumeGroup_GET_VOLUME_GROUP,
+					},
+				},
 			})
 	}