Update mobile backend article from Xamarin.Forms to .NET MAUI (#34679)

* Upgrade to .NET MAUI

* Edits.

* Edits.

* Fix code link.

Author: davidbritch

.openpublishing.publish.config.json

@@ -47,8 +47,8 @@
       "branch_mapping": {}
     },
     {
-      "path_to_root": "xamarin-forms-samples",
-      "url": "https://github.com/xamarin/xamarin-forms-samples",
+      "path_to_root": "maui-samples",
+      "url": "https://github.com/dotnet/maui-samples",
       "branch": "main",
       "branch_mapping": {}
     },
@@ -93,4 +93,4 @@
   "docs_build_engine": {
     "name": "docfx_v3"
   }
-}
+}