Add VolumeGroupSnapshot API definition, including CRD, client,

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

client/apis/volumegroupsnapshot/v1alpha1/doc.go

@@ -0,0 +1,20 @@
+/*
+Copyright 2023 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// +k8s:deepcopy-gen=package
+// +groupName=snapshot.storage.k8s.io
+
+package v1alpha1