Add support for multiple apps in one firebase project with flutter fire cli

[SedraPay]

This will be helpful when publishing the same code base as multiple white label apps (flavors/targets) with the same backend.

And the generated file would be similar to this:

  static const FirebaseOptions androidFirstFlavour = FirebaseOptions(
    ...
  );

  static const FirebaseOptions androidSecondFlavour = FirebaseOptions(
    ...
  );

  static const FirebaseOptions iosFirstFlavour = FirebaseOptions(
    ...
  );

  static const FirebaseOptions iosSecondFlavour = FirebaseOptions(
    ...
  );

And then we can call the related options object in the related main.dart