Workflow to create PR to update docs data model page

[anngvu]

In the Portal Design Working Group - Data Model Design presentation, when we discussed the "lighter-weight" design process for new assay templates, a contributor had a question of what templates were available. Currently, these are updated manually on the docs site and can fall behind pretty easily.

Unlike the NF and VEOIBD data model docs, we may not want to render GitHub pages and iframe the content into the docs. We want to write Markdown / MDX directly and make a pull request directly to the docs site.

Related to gf-dcc/docs#49.