I am talking about when you create a new blog with Tumblr, you can create your domain .tumblr.com, or when creating a deployment on Vercel or Netlify, you can have .vercel.app or *.netlify.appI get the gist that it's maybe using a wildcard sub-domain, and some API since the user can create it through the app, but how do you build or what tools do you use to build something like that?Or if you can point me out to where I can learn how to build something like that, I would be very grateful.