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/src/components/index.ts

@@ -26,6 +26,7 @@ export * from "./Feedback"
 export * from "./Feedback/Solutions"
 export * from "./Heading"
 export * from "./HooksLoader"
+export * from "./IconHeadline"
 export * from "./Icons"
 export * from "./InlineIcon"
 export * from "./InlineThemeImage"
@@ -73,5 +74,6 @@ export * from "./ThemeImage"
 export * from "./Toggle"
 export * from "./Tooltip"
 export * from "./TypeList"
+export * from "./VerticalCodeTabs"
 export * from "./WorkflowDiagram"
 export * from "./ZoomImg"