Fix image name for example webhook, and other nitpicks

Also bump example container versions to v3.0.0, and use
k8s.gcr.io/sig-storage instead of quay.io/k8scsi.

deploy/kubernetes/snapshot-controller/setup-snapshot-controller.yaml

@@ -25,7 +25,7 @@ spec:
       serviceAccount: snapshot-controller
       containers:
         - name: snapshot-controller
-          image: quay.io/k8scsi/snapshot-controller:canary
+          image: k8s.gcr.io/sig-storage/snapshot-controller:v3.0.0
           args:
             - "--v=5"
             - "--leader-election=false"