democratic-csi: Enable volume snapshot support

The _democratic-csi_ controller can create Synology LUN snapshots based
on VolumeSnapshot resources.  This feature can be used to e.g. create
data snapshots before upgrades, etc.

snapshot-controller/kustomization.yaml

@@ -0,0 +1,8 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+namespace: kube-system
+
+resources:
+- https://github.com/kubernetes-csi/external-snapshotter//client/config/crd?ref=v8.3.0
+- https://github.com/kubernetes-csi/external-snapshotter//deploy/kubernetes/snapshot-controller?ref=v8.3.0