Add script for generating schema in JSON format from YAML format

[pkalita-lbl]

Having a script that could convert from a source YAML schema to a JSON version would be useful for DataHarmonizer-based projects. This project already does that in its bootstrapping process, and it would furthermore be helpful for the projects that it generates to be able to do it as well (see pkalita-lbl/create-data-harmonizer#1). I think that means it would be useful to centralize such a script in this project. In a sense, this would be analogous to the scripts defined in https://github.com/linkml/linkml.