Consider replacing voluptuous with json-schema

[omad]

Although voluptuous is move expressive and more pleasant to write, json-schema is seeing renewed development in the last few months. It is progressing along a standardisation path, which means much stronger third party tooling including editor support with completions, and web based validation tools, and shared knowledge for developers, all of which make it worth considering for validating our configurations.

It's already used in datacube-core, and wouldn't be too hard to generate a schema using something like genson.