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/packages/docs-ui/package.json

@@ -60,7 +60,7 @@
     "react-dom": "^18.2.0"
   },
   "dependencies": {
-    "@medusajs/icons": "preview",
+    "@medusajs/icons": "rc",
     "@medusajs/ui": "^3.0.0",
     "@octokit/request": "^8.1.1",
     "@react-hook/resize-observer": "^1.2.6",