Add VolumeGroupSnapshot API definition, including CRD, client,

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

client/hack/README.md

@@ -26,7 +26,7 @@ Make sure to run this script after making changes to /client/apis/volumesnapshot
     ```
 * Checkout latest release version
     ```bash
-    git checkout v0.25.2
+    git checkout v0.26.0
     ```
 
 * Ensure the file `generate-groups.sh` exists
@@ -52,6 +52,40 @@ Once you run the script, you will get an output as follows:
     
 ```
 
+The following changes need to be made manually after running the above script:
+
+* The `SharedInformerFactory` interface in `./informers/factory.go` will have two functions named `Snapshot()`. Modify one to `GroupSnapshot()` and fix all references to that function in `informers/generic.go`.
+
+```bash
+	Snapshot() volumegroupsnapshot.Interface
+	Snapshot() volumesnapshot.Interface
+}
+
+func (f *sharedInformerFactory) Snapshot() volumegroupsnapshot.Interface {
+	return volumegroupsnapshot.New(f, f.namespace, f.tweakListOptions)
+}
+
+func (f *sharedInformerFactory) Snapshot() volumesnapshot.Interface {
+	return volumesnapshot.New(f, f.namespace, f.tweakListOptions)
+}
+```
+
+will become
+
+```bash
+	GroupSnapshot() volumegroupsnapshot.Interface
+	Snapshot() volumesnapshot.Interface
+}
+
+func (f *sharedInformerFactory) GroupSnapshot() volumegroupsnapshot.Interface {
+	return volumegroupsnapshot.New(f, f.namespace, f.tweakListOptions)
+}
+
+func (f *sharedInformerFactory) Snapshot() volumesnapshot.Interface {
+	return volumesnapshot.New(f, f.namespace, f.tweakListOptions)
+}
+```
+
 ## update-crd.sh
 
 NOTE: We need to keep both v1beta1 and v1 snapshot APIs but set served and storage version of v1beta1 to false. Please copy back the v1beta1 manifest back to the files as this script will remove it.
@@ -116,7 +150,7 @@ Update the restoreSize property to use type string only:
 
 * In `client/config/crd/snapshot.storage.k8s.io_volumesnapshots.yaml`, we need to add the `oneOf` constraint to make sure only one of `persistentVolumeClaimName` and `volumeSnapshotContentName` is specified in the `source` field of the `spec` of `VolumeSnapshot`.
 
-```
+```bash
               source:
                 description: source specifies where a snapshot will be created from. This field is immutable after creation. Required.
                 properties:
@@ -135,7 +169,7 @@ Update the restoreSize property to use type string only:
 
 * In `client/config/crd/snapshot.storage.k8s.io_volumesnapshotcontents.yaml `, we need to add the `oneOf` constraint to make sure only one of `snapshotHandle` and `volumeHandle` is specified in the `source` field of the `spec` of `VolumeSnapshotContent`.
 
-```
+```bash
               source:
                 description: source specifies from where a snapshot will be created. This field is immutable after creation. Required.
                 properties:
@@ -149,7 +183,7 @@ Update the restoreSize property to use type string only:
                 oneOf:
                 - required: ["snapshotHandle"]
                 - required: ["volumeHandle"]
-              volumeSnapshotClassName:
+              sourceVolumeMode:
 ```
 
 * Add the VolumeSnapshot namespace to the `additionalPrinterColumns` section. Refer https://github.com/kubernetes-csi/external-snapshotter/pull/535 for more details.