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/tailwind/theme-presets.js

@@ -99,7 +99,10 @@ const light = {
   "--docs-contrast-fg-secondary": "rgba(255, 255, 255, 0.56)",
   "--docs-contrast-border-base": "rgba(255, 255, 255, 0.16)",
   "--docs-contrast-border-top": "rgba(9, 9, 11, 1)",
-  "--docs-contrast-border-bot": "rgba(255, 255, 255, 0.1)",
+  "--docs-contrast-border-bot": "rgba(255, 255, 255, 0.10)",
+
+  "--docs-alpha-white-alpha-6": "rgba(255, 255, 255, 0.06)",
+  "--docs-alpha-white-alpha-12": "rgba(255, 255, 255, 0.12)",
 }
 
 const dark = {