Showcase registry

[igorkamyshev]

Now we manually add showcases to a particular page, it would be nice to have one config for showcase which will be used to inject a link to it to every related page.

Something like this 👇

// showcase/react-create-query/docs.ts

export default {
  name: "React + createQuery",
  articles: [
    "/api/factories/create-query/",
    "/integrations/react/use-query/"
  ]
}