Add refresh collections endpoint

Add utility endpoint for publishing every collection as it stands to Content API. (I needed to do this on CODE and figured it was quicker to just write this than do it manually, given how many were missing.)

The issue is when collections are initially created they are currently not published to Content API, but only once an item has been added. They're still in the fronts config, however, meaning the apps ask for them, but then break when Content API says they don't exist.

Will be submitting a separate pull request to fix that issue.