Add APIs audio encoder/decoder factories in PeerConfigurer

In Meta we have our own audio encoder/decoder factories and we would like to exercise those in the peer connection e2e test framework.
Also, looks cleaner to have the APIs for both video and audio :)

Bug: webrtc:14910
Change-Id: Ibd1e0f39fc809882ef17b3de3154fdf4b567013b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/293782
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Jeremy Leconte <jleconte@webrtc.org>
Reviewed-by: Jeremy Leconte <jleconte@google.com>
Cr-Commit-Position: refs/heads/main@{#39328}