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/book/app/learn/advanced-development/modules/page.mdx

@@ -0,0 +1,15 @@
+export const metadata = {
+  title: `${pageNumber} Modules Advanced Guides`,
+}
+
+# {metadata.title}
+
+In the next chapters, you'll learn more about developing modules and related resources.
+
+By the end of this chapter, you'll know more about:
+
+1. A module's container and how a module is isolated.
+2. Passing options to a module.
+3. The service factory and the methods it generates.
+4. Using a module's service to query and perform actions on the database.
+5. Using multiple services in a module.