Build out apis.json file from a folder of individual API definitions

[jeskew-gov]

The current jekyll site uses a static apis.json file to which new APIs are added by pull request. Because git doesn't understand that a PR's intent is just to add an element to the end of the list, it's really easy to create merge conflicts between unrelated PRs. These need to be manually fixed, and line-by-line fixes on merge conflicts seem like a good vector for mangling data.

I think it would be better if individual API definitions were stored as separate files in a folder that is then combined to form apis.json as part of the jekyll build.

[jeskew-gov]

According to https://help.github.com/en/github/working-with-github-pages/about-github-pages-and-jekyll#plugins, we wouldn't be able to use a custom plugin as part of the GitHub pages build. This change would require building the site and committing static HTML pages or running a script to build the apis.json file in CI or before committing.