Draft: Add audio-group utils to group audio streams

This MR adds an audio-group-utils.lua utility script that groups audio stream nodes by systemd cgroups, so that applications can easily change the volume of a set of audio nodes that are part of the same group, and also redirect them to a different device all at once.

This MR is still a work in progress, and more changes will be added such as an option to enable this behavior, and also a way to hide the actual audio stream nodes so that only the respective loopback stream nodes are shown.