Action to create pages in the correct place

[zkamvar]

Right now, the user must manually create the site after the branches are set up. Luckily, GitHub has a method for creating sites through the API, so we can add a small action that does that if the page does not exist.

This will definitely make it easier for contributors

[zkamvar]

It turns out that this is not possible from github actions itself. Instead, an app is needed, which may be addressable with the SANDPAPER_WORKFLOW token.