New RFC PR: Test Kitchen Multi-Server Testing

We’ve been talking about this for years, I decided to finally put (virtual) pen to paper and lay out how I think we can add multi-server capabilities to Test Kitchen. If that’s a thing you have opinions on, please check out the document and PR thread, even if you aren’t a Chef or TK developer. I want to make sure we are actually going to do this in a way that will work for all TK users.