Add missing ServiceAccount in snapshot-validation-deployment

Deployment manifest of snapshot-validation-deployment was missing a
service account and hence was using the default one that exists in
kube-system namespace.
This caused it to log Failed to watch *v1.VolumeSnapshotClass

upup/models/cloudup/resources/addons/snapshot-controller.addons.k8s.io/k8s-1.20.yaml.template

@@ -1218,6 +1218,7 @@ spec:
         - name: snapshot-validation-webhook-certs
           secret:
             secretName: snapshot-validation-secret
+      serviceAccountName: snapshot-controller
 ---
 apiVersion: v1
 kind: Service