Notifications system

For inspiration https://www.delightfulengineering.com/blog/nest-websockets/rooms

For notifications, let's use Pusher after all. It's quite alright and will make things faster and it's not super complicated to replace it later.

For React Query https://jonbellah.com/articles/websockets-with-react-query

The idea here is to have notifications, where user would be able to get a notification in real time.