Add PipeWire support on Linux

To quote the PipeWire website (https://pipewire.org/#about):

"PipeWire is a project that aims to greatly improve handling of audio and video under Linux. It aims to support the usecases currently handled by both PulseAudio and Jack and at the same time provide same level of powerful handling of Video input and output. It also introduces a security model that makes interacting with audio and video devices from containerized applications easy, with supporting Flatpak applications being the primary goal. Alongside Wayland and Flatpak we expect PipeWire to provide a core building block for the future of Linux application development.

Features include:

• Capture and playback of audio and video with minimal latency.
• Real-time Multimedia processing on audio and video.
• Multiprocess architecture to let applications share multimedia content.
• GStreamer plugins for easy use and integration in current applications.
• Sandboxed applications support.

See Flatpak for more info."

@pgorley What do you think?