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/resources/app/recipes/multi-region-store/page.mdx

@@ -157,7 +157,7 @@ By integrating a third-party Content Management Systems (CMS), you benefit from
 To integrate a third-party system, create a custom module whose main service connects to that third-party service.
 
 <Card
-  href="!docs!/basics/modules"
+  href="!docs!/learn/basics/modules"
   title="Create a Module"
   text="Learn how to create a module in Medusa."
   icon={AcademicCapSolid}