Chapter 3: Install Firebase Auth

• Here we move our Stack into a single component.
• We also install firebase in packages/app, and @react-native-firebase/auth + @react-native-firebase/app in apps/expo
  • libraries with native code must be installed in apps/expo
  • Finally, we initialize our Firebase code

Up next: create our apps on Firebase's website, and add the credentials for iOS, Android and Web.