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.

democratic-csi/storageclass.yaml

@@ -9,3 +9,11 @@ parameters:
   csi.storage.k8s.io/provisioner-secret-namespace: democratic-csi
   csi.storage.k8s.io/node-stage-secret-name: synology-iscsi-chap
   csi.storage.k8s.io/node-stage-secret-namespace: democratic-csi
+
+---
+apiVersion: snapshot.storage.k8s.io/v1
+kind: VolumeSnapshotClass
+metadata:
+  name: synology-iscsi
+driver: org.democratic-csi.iscsi-synology
+deletionPolicy: Delete