Add ImageVolumeSource API

Adding the required Kubernetes API so that the kubelet can start using
it. This patch also adds the corresponding alpha feature gate as
outlined in KEP 4639.

Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

pkg/apis/core/zz_generated.deepcopy.go

@@ -2044,6 +2044,22 @@ func (in *ISCSIVolumeSource) DeepCopy() *ISCSIVolumeSource {
 	return out
 }
 
+// DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
+func (in *ImageVolumeSource) DeepCopyInto(out *ImageVolumeSource) {
+	*out = *in
+	return
+}
+
+// DeepCopy is an autogenerated deepcopy function, copying the receiver, creating a new ImageVolumeSource.
+func (in *ImageVolumeSource) DeepCopy() *ImageVolumeSource {
+	if in == nil {
+		return nil
+	}
+	out := new(ImageVolumeSource)
+	in.DeepCopyInto(out)
+	return out
+}
+
 // DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
 func (in *KeyToPath) DeepCopyInto(out *KeyToPath) {
 	*out = *in
@@ -6477,6 +6493,11 @@ func (in *VolumeSource) DeepCopyInto(out *VolumeSource) {
 		*out = new(EphemeralVolumeSource)
 		(*in).DeepCopyInto(*out)
 	}
+	if in.Image != nil {
+		in, out := &in.Image, &out.Image
+		*out = new(ImageVolumeSource)
+		**out = **in
+	}
 	return
 }