Play notification sound when new message received by idle or out of focus client window

[amalg]

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Is your feature request related to a problem? Please describe.
The number one usability issue with Nextcloud Talk in my opinion is the lack of notification sound when a new message is received in any conversation thread by the desktop client when it is idle or not the focused window. This also applies to browser tabs but this repo is for the desktop client, so I will keep my focus there. In short, the issue is that Nextcloud Talk does not hook any notifications into the Nextcloud Notifications system, so on the web under /settings/user/notifications, there are no activities listed for "new message", only "invited to a conversation". The desktop client settings -> sounds section also only offers "Play sounds when participants join or leave a call", but new messages sent to me while my focus is on another window go completely unnoticed due to this lack of audible notification.

Describe the solution you'd like
I would like the Nextcloud Desktop Client for Win32/64 to support notification sounds for new messages that arrive while the client is idle or not currently in focus. While the client window is in focus, sounds should only be played for new messages arriving if the window has been idle (no activity from the user) for a configurable amount of time (5 mins default). Ideally, the desktop client would register various events with Windows OS for as "system sounds" so the user could configure what sound (if any) plays for which event via Windows. Clicking a "Set sounds" link in the client application could open Windows Sounds settings for the user.

Describe alternatives you've considered
Alternatively the client could allow for configuration of event types and sounds that play within itself and not register program events with Windows Sounds, but sound alerts of some type for new message arrival to an idle or out of focus client window is an absolute must to make Nextcloud Talk a serious option as a personal and enterprise communication channel.