Investigate and maybe migrate admin

[beechnut]

The admin folder has a config and index file for Netlify CMS.

First: do we use Netlify for the 18F site? If we do, we should migrate it to maintain functionality. If not, we should add it to #3864.

To the replatform-main branch, we copied the 18f/guides settings, so we should start by diffing that and main's config/index. It seems like index has Jekyll-style settings (e.g. site.baseurl), so we should replace those as necessary.

Also, it looks like the config file defines settings and YAML fields — we've renamed some of them (like image_accessibility is now image_alt).

Tasks

Beta Give feedback

1. Admin works equivalently to how it did in the Jekyll framework