[Feature] Dbus method for getting all notification

Currently only the `uint count, bool dnd, bool cc_open, bool inhibited` can be get from the DBus interface. It would be great if there would be an other method (or signal or both) that can be used to get all the notifications as presented in the Control Center.

I want to extend my custom waybar component so I could display the notification icons next to the notification number.

Start by locating the DBus interface that exposes count, dnd, cc_open, and inhibited, then trace how notifications are represented for the Control Center. Decide whether a method, signal, or both should expose the displayed notifications, and verify that the result supports the custom waybar use case.

Written by the indexing model from the issue text.