docs: add routing page (#9550)

- Add a new homepage to `book` project for the routing page
- Move all main doc pages to be under `/v2/learn` (and added redirects + fixed links across docs)
- Other: add admin components to resources dropdown + fixes to search on mobile.

Closes DX-955

Preview: https://docs-v2-git-docs-router-page-medusajs.vercel.app/v2

www/apps/api-reference/components/DownloadFull/index.tsx

@@ -9,11 +9,7 @@ const DownloadFull = () => {
 
   return (
     <Button variant="secondary">
-      <Link
-        href={`${process.env.NEXT_PUBLIC_BASE_PATH}/download/${area}`}
-        download
-        target="_blank"
-      >
+      <Link href={`/api/download/${area}`} download target="_blank">
         Download OpenApi Specs Collection
       </Link>
     </Button>