chore: add examples directory

[pi0]

Initialize examples directory. Examples are valid packages that can be used standalone or in the workspace each featuring a nuxt core feature.

Initial examples:

• async-data
  • known issue: in workspace/stub $fetch type is not detected
• hello-world
  • known issue: pages is mandatory and makes warning
• pages
• with-vite
  • Might be with-webpack once vite was stable enough for dev

Usage: yarn example [name] (yarn example pages) (name should match package.json name field. hello-world => example-hello-world)

Once we had nuxt/design ready, we can also make them consistently fancier using it's UI kit :)