Add VolumeGroupSnapshot API definition, including CRD, client,

informer and lister generated code.
Update ./client/hack/README with instructions to update the client
directory.

client/config/crd/snapshot.storage.k8s.io_volumesnapshots.yaml

@@ -3,8 +3,8 @@ apiVersion: apiextensions.k8s.io/v1
 kind: CustomResourceDefinition
 metadata:
   annotations:
-    controller-gen.kubebuilder.io/version: v0.8.0
-    api-approved.kubernetes.io: "https://github.com/kubernetes-csi/external-snapshotter/pull/665"
+    controller-gen.kubebuilder.io/version: v0.11.3
+    api-approved.kubernetes.io: "https://github.com/kubernetes-csi/external-snapshotter/pull/814"
   creationTimestamp: null
   name: volumesnapshots.snapshot.storage.k8s.io
 spec:
@@ -188,6 +188,10 @@ spec:
                   specified, it indicates that the size is unknown.
                 pattern: ^(\+|-)?(([0-9]+(\.[0-9]*)?)|(\.[0-9]+))(([KMGTPE]i)|[numkMGTPE]|([eE](\+|-)?(([0-9]+(\.[0-9]*)?)|(\.[0-9]+))))?$
                 x-kubernetes-int-or-string: true
+              volumeGroupSnapshotName:
+                description: VolumeGroupSnapshotName is the name of the VolumeGroupSnapshot
+                  of which this VolumeSnapshot is a part of.
+                type: string
             type: object
         required:
         - spec