Several stability improvements / edge case handling along with stereo Opus support

Added

• Supervisor framework to improve edge case & error handling #1005 #1006 #1010 #1017
• Support for stereo Opus tracks #1013
• Allow CORS responses to be cached to allow faster initial connection #1027

Fixed

• Fixed SSRC mix-up for simulcasted tracks during session resume #1014
• Fixed screen corruption for non-simulcasted tracks, caused by probing packets #1020
• Fixed Handling of Simple NALU keyframes for H.264 #1016
• Fixed TCPMux & UDPMux mixup when multiple host candidates are offered #1036

Changed

• Webhook requests are now using Content-Type application/webhook+json to avoid eager JSON parsing #1025
• Don't automatically add STUN servers when explicit Node IP has been set #1023
• Automatic TCP and TURN/TLS fallback is now enabled by default #1033

Removed

• Fully removed references to VP9. LiveKit is focused on AV1. #1004