Register FCM Token For The Device For Every Successful Login

[chaiwa-berian]

To ensure the user receives notifications to whatever device they login into, send a request to the server to register the Firebase Cloud Messaging Token(FCM Token) for the device.

If the FCM token gets revoked(either via the web interface or fcm console), server should notify clients. Client should run service(background recommended) to re-submit the new token for the authenticated user.

Client UI can show whether server notifications are on or off for a given device(i.e. whether the device's fcm token is registered or not):- This way the user can be able to force-resubmit the token.