Push Notifications

[PJprogrammer]

Is your feature request related to a problem? Please describe.
Users need to be instantly notified when a new announcement has been made. (Especially important issue now that the hackathon is strictly online)

Describe the solution you'd like
Use Firebase to send push notifications whenever a new announcement is made.

Implementation:
Receive push notifications by subscribing to a particular topic

When the app is in the background or terminated, the push notification will show in the notification tray. However, if the app is in the foreground, no notification will show; in this case, use the local notifications in order to mimic the behavior of push notifications.

Describe alternatives you've considered

Additional context

[github-actions]

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