webrtc: support reading and proxying stereo PCMU/PCMA tracks

[aler9]

TODO:

• error message in Firefox and in all browsers that do not support this

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 50 lines in your changes are missing coverage. Please review.

Project coverage is 54.00%. Comparing base (6da8aee) to head (6d542dd).

Files	Patch %	Lines
internal/protocols/webrtc/outgoing_track.go	0.00%	30 Missing ⚠️
internal/protocols/webrtc/incoming_track.go	0.00%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3402      +/-   ##
==========================================
- Coverage   54.06%   54.00%   -0.07%     
==========================================
  Files         190      190              
  Lines       18847    18879      +32     
==========================================
+ Hits        10190    10195       +5     
- Misses       7858     7885      +27     
  Partials      799      799              

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[github-actions]

This issue is mentioned in release v1.8.3 🚀
Check out the entire changelog by clicking here