initalizeFlipper should be set in template app by default (#27569)

Summary:
Issue: https://github.com/facebook/react-native/issues/27565

initalizeFlipper should be set in template app by default.

## Changelog

[iOS] [Changed] - Added Flipper to template app
[Android] [Changed] - Added Flipper to template app
Pull Request resolved: https://github.com/facebook/react-native/pull/27569

Test Plan:
Connect Flipper to the iOS application
Connect Flipper to the Android application

Reviewed By: passy

Differential Revision: D19344704

Pulled By: rickhanlonii

fbshipit-source-id: ca126fd2caab13751ddc2ce6d195bd0c644c704e

template/android/app/src/main/java/com/helloworld/MainApplication.java

@@ -44,6 +44,7 @@ public class MainApplication extends Application implements ReactApplication {
   public void onCreate() {
     super.onCreate();
     SoLoader.init(this, /* native exopackage */ false);
+    initializeFlipper(this, getReactNativeHost().getReactInstanceManager());
   }
 
   /**

template/ios/HelloWorld/AppDelegate.m

@@ -19,6 +19,7 @@
 
 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
 {
+  [AppDelegate initializeFlipper:application];
   RCTBridge *bridge = [[RCTBridge alloc] initWithDelegate:self launchOptions:launchOptions];
   RCTRootView *rootView = [[RCTRootView alloc] initWithBridge:bridge
                                                    moduleName:@"HelloWorld"