feat: allow customizing the index and head

packages/desktop/src/index.html

@@ -3,13 +3,10 @@
   <head>
     <title>Dioxus app</title>
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <!-- CUSTOM HEAD -->
   </head>
   <body>
     <div id="main"></div>
-    <script>
-      import("./index.js").then(function (module) {
-        module.main();
-      });
-    </script>
+    <!-- MODULE LOADER -->
   </body>
 </html>