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/config/index.ts

@@ -4,7 +4,7 @@ import { sidebarConfig } from "./sidebar"
 const baseUrl = process.env.NEXT_PUBLIC_BASE_URL || "http://localhost:3000"
 
 export const config: DocsConfig = {
-  titleSuffix: "Medusa v2 Docs",
+  titleSuffix: "Medusa v2 Documentation",
   baseUrl,
   basePath: process.env.NEXT_PUBLIC_BASE_PATH,
   sidebar: sidebarConfig,