[Feature] Show inhibited/dnd notifications once inhibiting/dnd is over

[ItsDrike]

Is your feature request related to a problem? Please describe.
I like to set an inhibitor when my lockscreen is on, so the notifications don't appear on top, however, once I unlock my machine and unset that inhibitor, I don't know whether I missed some notifications or not.

Similarly, I have a keybind to toggle dnd mode, but again, once I leave dnd, I don't know whether I missed any notifications or not.

Describe the solution you'd like
It'd be great if the notifications that I missed while inhibited/dnd were all shown at once once the inhibiting/dnd is over.

This is actually the behavior that dunst uses when leaving paused mode (dunstctl set-paused).

Describe alternatives you've considered
It would technically probably be possible to script this, capturing all notifs & checking if inhibit/dnd is true, if so, storing that notif and dismissing it. Another script that listens to the inhibit/dnd state would then need to re-emit the missed notifications.

Scripting all this would however be pretty non-trivial and it wouldn't be completely ideal anyways, because you would loose the time information on when the notif got sent.

Additional context
The only potential issue I see here is that there could be a lot of notification that would suddenly all show up at once, and follow the default timeout, which means there'd be basically no way for the user to read them in time. IMO this is fine, as they'll still be in the notification center and it will make it clear that there were some missed notifications.

As an alternative, there could just be a single notification with something like "20 missed notifications".

It may be also useful to also have a way to separate the missed notifications from the rest in the notification center, to make them easier to find.

This is somewhat related to #275, which talks about disabling the timeout for notifications when idle, perhaps it could even cover this problematic by treating those notifications received when idle as missed and once user is no longer idle, they would just get re-emitted. That said, I think disabling the timeout during idle is probably still a better option.