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/debugging-and-testing/page.mdx

@@ -0,0 +1,12 @@
+export const metadata = {
+  title: `${pageNumber} Debugging and Testing`,
+}
+
+# {metadata.title}
+
+In the next chapters, you’ll learn about the tools Medusa provides for testing and debugging your Medusa application.
+
+By the end of this chapter, you’ll learn:
+
+- How to use Medusa's `medusa-test-utils` test to write integration tests.
+- How to use Medusa’s `Logger` utility to log messages.