[kde-telephony-daemon] Pause media players on incoming call

When receiving a call you want to be able to talk without any playing
music interfering.
Also you want to hear the actual ringtone instead of the music.

Pause all media players when a call is received.
Unpause them when you reject a call.

Initial work: https://invent.kde.org/plasma-mobile/plasma-dialer/-/
merge_requests/66

Implemented with https://github.com/sailfishos/qtmpris/

Contributes to #24



Co-Authored-By: Nicolas Fella <nicolas.fella@gmx.de>