Test on WP Playground

[jazzsequence]

We could add a workflow like the one discussed here (Gist) to add a comment to PRs with a link to a demo of the site on the WP playground. This would obviously only work for WP plugins. There might be some devil in the details things that come up if we try to implement this given his notes about CORS from GitHub.

The notes also indicate that this is for plugins that don't have a build step -- which is true for most of our plugins, but we might want to build out a step before this one to create a zip file that gets passed along after a build has been run.