Generate Gihub Pages with Github Actions

[bamthomas]

This PR is for generating a GH pages web site with the models.

It uses mkdocs with a slightly updated mkdocs-json-schema-plugin.

You can see what it's like on the forked repo : https://bamthomas.github.io/BoAmps/

The following changes have been made:

1. add a pyproject.toml to use python
2. add doc/mkdocs.yml that is describing how to make the site to mkdocs
3. add doc/gen_pages.py that will reuse resources and README.md
4. add doc/docs/model templates files
5. finally add the github workflow to generate GH pages

If you merge it you will have to change

site_url: https://bamthomas.github.io/BoAmps/

in mkdocs.yml to https://boavizta.github.io/boamps

It is possible eventually to configure a more fancy url like https://boamps.boavizta.org.

TODO: there is a little bug in the model generated pages that are not folding/unfolding.