Using JSON input for model pages

[cpalfonso]

@dansand the existing model input markdown files have been converted to JSON as a proof of concept in commit 71a3199. The json-input-test branch is deployed on Netlify here; each model in the list also has a JSON version. It wasn't a lot of work to move from the markdown YAML to JSON, so it hopefully shouldn't be too hard to use the RO-Crate files either.