docs: change navbar items + breadcrumb improvements (#9209)

- Add a new commerce module navbar item
- Rename Learning Resources to Development Resources (in navbar and across documentation content)
- Improve breadcrumbs to show categories / subcategories

Preview: https://resources-docs-git-docs-navbar-changes-medusajs.vercel.app/v2/resources

www/apps/ui/src/app/not-found.mdx

@@ -25,7 +25,7 @@ If you think this is a mistake, please [report this issue on GitHub](https://git
       icon: BookOpen
     },
     {
-      title: "Learning Resources",
+      title: "Development Resources",
       href: "!resources!",
       icon: AcademicCapSolid
     },

www/apps/ui/src/app/not-found.tsx

@@ -35,7 +35,7 @@ export default function NotFound() {
             icon: BookOpen,
           },
           {
-            title: "Learning Resources",
+            title: "Development Resources",
             href: "!resources!",
             icon: AcademicCapSolid,
           },