Revert removal of firebase_options.dart

Someone using the example app and is only interested in iOS may not
have flutterfire installed hence this file may not be generated. To
prevent the app from crashing in that case, we provide this

Author: vickz84259

examples/push_notifications/lib/firebase_options.dart

@@ -0,0 +1,57 @@
+// File generated by FlutterFire CLI.
+// ignore_for_file: lines_longer_than_80_chars, avoid_classes_with_only_static_members
+import 'package:firebase_core/firebase_core.dart' show FirebaseOptions;
+import 'package:flutter/foundation.dart'
+    show defaultTargetPlatform, kIsWeb, TargetPlatform;
+
+/// Default [FirebaseOptions] for use with your Firebase apps.
+///
+/// Example:
+/// ```dart
+/// import 'firebase_options.dart';
+/// // ...
+/// await Firebase.initializeApp(
+///   options: DefaultFirebaseOptions.currentPlatform,
+/// );
+/// ```
+class DefaultFirebaseOptions {
+  static FirebaseOptions get currentPlatform {
+    if (kIsWeb) {
+      throw UnsupportedError(
+        'DefaultFirebaseOptions have not been configured for web - '
+        'you can reconfigure this by running the FlutterFire CLI again.',
+      );
+    }
+    switch (defaultTargetPlatform) {
+      case TargetPlatform.android:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions have not been configured for android - '
+          'you can reconfigure this by running the FlutterFire CLI again.',
+        );
+      case TargetPlatform.iOS:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions have not been configured for ios - '
+          'you can reconfigure this by running the FlutterFire CLI again.',
+        );
+      case TargetPlatform.macOS:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions have not been configured for macos - '
+          'you can reconfigure this by running the FlutterFire CLI again.',
+        );
+      case TargetPlatform.windows:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions have not been configured for windows - '
+          'you can reconfigure this by running the FlutterFire CLI again.',
+        );
+      case TargetPlatform.linux:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions have not been configured for linux - '
+          'you can reconfigure this by running the FlutterFire CLI again.',
+        );
+      default:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions are not supported for this platform.',
+        );
+    }
+  }
+}

examples/push_notifications/lib/main.dart

@@ -5,9 +5,12 @@ import 'firebase_options.dart';
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
-  await Firebase.initializeApp(
-    options: DefaultFirebaseOptions.currentPlatform,
-  );
+
+  if (Platform.isAndroid) {
+    await Firebase.initializeApp(
+      options: DefaultFirebaseOptions.currentPlatform,
+    );
+  }
 
   await Talk.registerPushNotificationHandlers(
     androidChannel: const AndroidChannel(