Add 'collaborator' field, Alice to the a11y article

As a follow-up to #347, this adds Alice to the authors list and introduces a collaborator field for when we want to include a co-author for an article.

There are a few different ways this could be handled. We could either include this new field or move over to supporting multiple authors (e.g `author` could be `authors`, an array of authors that we loop over).

reviewer: @ebidel