Most of the desktop environments will spawn pulseaudio, but we can instead simply run it as a systemd service instead.
This patch also makes the system wide service run in foreground as recommended by the systemd projects and allows it to use sd_notify to signal ready instead of reading a pid written to a file. It is now also restarted on failure.
The user version has been tested with KDE and works fine there.
The system-wide version runs, but I haven't actually used it and upstream does not recommend running in this mode.
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