Add ability to subscribe to updates

[Battlesquid]

With the ongoing efforts to transform the webapp into a PWA (#11), it would be good to think about how to leverage the additional features PWAs offer, one being push notifications. Some things they could be used for include:

• Allowing users to subscribe to updates, specifically, be notified when questions from certain authors are answered, which would especially be useful for users who ask questions on the Q&A.
• Notifying users when new questions are asked
• Notifying users when the Q&A is opened/closed (depends on Add cron job for checking when a new Q&A forum is open #6)

Implementing this would most likely leverage Supabase Realtime. This is already used by the bot to detect when questions are answered, but additional logic would be required for the latter two use cases.

The added benefit of implementing this is being able to frequently update the questions store in the webapp's indexeddb instance with smaller batches of data. This may completely eliminate the current method of updating indexeddb, which is refreshed every 6 hours.