Make a dedicated package for job_extract_chroma

[CharlesHolbrow]

I'm in the process of making pytorch and torchaudio optional dependencies. However, the support for the ChromaExtractor is a little sloppy, and it should just be moved into its own dedicated job that always requires torchaudio.

[CharlesHolbrow]

TODOs:

• [x] update example CLI invocation in README
• [x] QA
• [x] double check docker container validity