feat: Implement backend for notifications

[Doraemon012]

Is your feature request related to a problem? Please describe.

Implement the backend for in-app notifications.

Describe the solution you'd like

• Store a users' notifications in the user object in firebase.
• A notification object should be similar to this:

  {
  title: "Title of notification",
  text: "Text to be displayed", // (eg. The event `Summer Camp 2024`  has been deleted)
  date: timestamp(),
  link: url() // (new url of the event, if it is rescheduled)
  }

• A user should receive notification when the users' registered event is deleted.
• The displayed notifications should be sorted by time.
• The notification should be automatically deleted after 7 days.

Describe alternatives you've considered

None

Additional context

None.

[nishant0708]

hey @Tanay-ErrorCode @Doraemon012 can i work on this issue?

[Tanay-ErrorCode]

@nishant0708 Go ahead.