docs: migrate UI docs (#13245)

* docs: create a new UI docs project (#13233)

* docs: create a new UI docs project

* fix installation errors

* docs: migrate UI docs content to new project (#13241)

* Fix content

* added examples for some components

* finish adding examples

* lint fix

* fix build errors

* delete empty files

* path fixes + refactor

* fix build error

www/apps/ui/specs/examples/button-loading.tsx

@@ -0,0 +1,5 @@
+import { Button } from "@medusajs/ui"
+
+export default function ButtonLoading() {
+  return <Button isLoading={true}>Button</Button>
+}