Add github action for Messaging (#4970)

Example/watchOSSample/SampleWatchAppWatchKitExtension/InterfaceController.swift

@@ -0,0 +1,28 @@
+// Copyright 2020 Google
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import SwiftUI
+import FirebaseStorage
+
+class InterfaceController: WKInterfaceController {
+  @IBOutlet var imageView: WKInterfaceImage!
+
+  override func willActivate() {
+    let storage = Storage.storage()
+    let storageRef = storage.reference().child("sparky.png")
+    storageRef.getData(maxSize: 20 * 1024 * 1024) { (data: Data?, error: Error?) in
+      self.imageView.setImageData(data)
+    }
+  }
+}