Add Expo config plugin for messaging module [iOS]

[bazter]

Hello, I'd like to request an expo config plugin, that would modify the AppDelegate.mm file according to docs.

The change consists of two lines I have to manually add every time I run expo prebuild --clean:

//AppDelegate.mm

// top of the file
#import "RNFBMessagingModule.h"

// inside the body of didFinishLaunchingWithOptions
self.initialProps = [RNFBMessagingModule addCustomPropsToUserProps:nil withLaunchOptions:launchOptions];

This change is needed if we'd like to skip unnecessary app bootstrap during background notifications on iOS.
The provided snippet is from latest RN (0.71.x) and it was actually a bit different before, so some backward compatibility might be needed for older react-native versions.

The plugin could be similar to the one from the app module, which does very similar modification. For reference, please see @react-native-firebase/app/plugin/src/ios/appDelegate.ts

[mikehardy]

Expo plugins are community supported, if you propose a PR implementing a new plugin, we can merge it.