Allow Project Owners to submit projects for code inventory file

We should consider creating a form on the code.mil website that allows project owners to submit details of their projects for the purposes of generating the code.json inventory file.

The steps toward this goal might involve…

• breaking the existing code.json file into project-specific data files (e.g. src/_data/code_json/move-mil.json (or YAML…?) (#232)
• add small Jekyll plugin to generate code.json file from data files (#232)
• determine a means of validating individual project data files and the resultant code.json file
• create the necessary pages on code.mil website to accept these submissions (this one's worth its own issue for sorting out design, implementation, etc.)
• form submission could/should create a pull request on this project's repository for evaluation and inform the user of the PR's URL (on say, a "thanks!" page)

Possibly useful Netlify documentation:

• https://www.netlify.com/docs/form-handling/
• https://www.netlify.com/docs/functions/