Fix stereo audio for Chromium-based browsers (perhaps WebRTC SDP issue)

Musicbots like “Jockie Music” stream stereo audio, but chromium-based webbrowsers won't decode it as stereo.

This might be, because the “stereo=1” or “sprop-stereo=1” media type parameters are missing in the WebRTC SDP.

An unrelated project taught me that Firefox will decode stereo streams even without these parameters set, while Chrome is always downmixing the channels to mono when these parameters are not set.

I tested streaming stereo audio with “Jockie Music” on the following systems:

• fresh Windows 10 VM with Edge → MONO
• fresh Windows 10 VM with Chrome → MONO
• fresh Windows 10 VM with Firefox → STEREO
• fresh Windows 10 VM with native Discord Desktop client → STEREO