Push and notification improvements

[manuroe]

This is a meta issue to quickly list things to solve. Corresponding issues will be created:

Push technical issues

• e2ee keys lost in the push extension. The app never got them
• Out of memory errors in push extension
• Request com.apple.developer.pushkit.unrestricted-voip to Apple
• Or consider this other entitlement, com.apple.developer.usernotifications.filtering, to hide unexpected notifications
• Use /event again and throttle /sync requests if we can

Notification UX issues

• Notifications: User display name or avatar changes are displayed as invites #4659
• "Message" is the fallback notification for too many things #4653
  • Have dedicated notifications for reactions
  • Notice events
  • Have dedicated notifications for errors: "Sorry, we failed to fetch the message content, open the app", etc
• Improve notification message for replies. #4660
• Have dedicated notifications for media
• Consider appropriate content (or silence) notifications from mention-only rooms when not mentioned (discussion).
• Dismiss "Notification" notifications when another comes in to avoid stacking.
• Have notification for invite (not sure if it works)
• Support upcoming iOS 15 notification avatars #4710 (pending Xcode 13 support in the project and on CI).

Later:

• Hide "Message" or improve notifications for technical events. Will be fixed with unrestricted-voip
• Have more actions (e.g. accept/decline room invites)