Add support for bitrate in sox_io backend

soxi shows the files bitrate, but I'm pretty sure torchaudio.info doesn't when using the sox_io backend.

🚀 Feature

Create functionality within torchaudio.info and the AudioMetadata object to be able to determine a files bitrate.

Motivation

I want to be able to easily determine the bitrate within torchaudio so that I can do EDA and see if bitrate of audios has an impact on inference (e.g. if train set audios are all high bitrate but inference is low bitrate, will it lower accuracy?) If so then knowing the bitrates of the audios is important so that you can do proper augmentation to prevent the decreased accuracy.

Pitch

soxi shows bitrate, but as far as I can tell, torchaudio.info using the sox_io backend doesn't. Make torchaudio.info have the same data as soxi when using the sox_io_backend

Alternatives

I tried doing this outside of torchaudio with pydub, mutagen, file (command line) and soxi but it would be better if everything could be done with torchaudio. Thank you.

Additional context

Start with the torchaudio.info and AudioMetadata entry points, then compare the sox_io metadata they expose with the bitrate reported by soxi. Done means torchaudio.info using sox_io can determine and expose a file's bitrate through AudioMetadata.