ENH: schema description and validation for YAML file

[jerdra]

Niviz uses a YAML configuration file in order to construct arguments for building images and outputting into a BIDS folder.

This YAML is expected to be structured in a certain way (enforced in code) but isn't explicitly encoded anywhere. This gap would be well-served by a YAML schema validator that is run as a first step (and is provided as separate functionality as a CLI tool packaged with Niviz).

https://github.com/23andMe/Yamale

Looks like an option