Separate Firebase Notifications into separate package

[adar2378]

Currently, the firebase_cloud_messaging related logics are inside the djangoflow_app package. We need to separate the firebase_cloud_messsaging logics into a separate package.

The simplified purpose of this is to

• listen for new/initial FCM messages
• get pushToken from FCM

Potential solution:

• Notification listener widget (onMessage, onInitialMessage callbacks) More information: https://firebase.google.com/docs/cloud-messaging/flutter/receive#handling_interaction
• Utility methods for checking/requesting notification permission. With optionally app_settings for rejected permission. So that user can go to the app's notification settings and enable it.
• Maybe a callback too for firebase token retrieval done with the Notification listener widget. So that we can also send this token to our backend server.

Bonus Task:

• Create unit tests for the separate package

[adar2378]

Create a new package with following requirements.

1. The firebaseNotificationHandler widget should have callbacks, onMessage, onMessageTap
2. Streams need to listen to FirebaseMessaging.onMessageOpenedApp, FirebaseMessaging.onMessage.
3. FirebaseMessaging.instance.getInitialMessage() this we will need to call only once in app.
4. We need to listen to onTokenRefresh from FirebaseMessaging.
5. And there should a callBack which will return the token when it’s available. Even better if this callback can be triggered through a method something like DjangoflowFCMHanlder.getToken
6. Request notification permission through FirebaseMessaging object’s requestPermission method

check this for reference https://pub.dev/packages/firebase_notifications_handler