[Feature] Notifications for each specific user

Hi!

I'm currently really liking the new (i think new?) notification system which uses Apprise, but it would be nice if I could set separate notification methods, for each specific user, and tell them when their selected item was downloaded, and not others.

An example of this would be if User1 started watching a Venom, and once it's downloaded, it sends a notification to just User1, using the notification service setup for them, in this case an email. If User2 started watching Spiderman, then once it's finished, User2 will receive a notification from their specified service, in this case discord webhook.

I'm not a developer by any means, so I have no idea if this is possible, or the difficulty of implementation, but I thought it would be a nice feature when Nefarious is being used by multiple users.

Thanks!

Start by tracing the Apprise notification flow and how users, watched items, and completed downloads are related. Define how each user's notification service and selected items should be associated, then verify that a download notification reaches only the relevant user through their chosen service.