append custom_script_tags_str to the HTML of homepage

src/backend/src/services/PuterHomepageService.js

@@ -311,6 +311,9 @@ class PuterHomepageService extends BaseService {
 
     <body>
         <script>window.puter_gui_enabled = true;</script>
+        ${
+            custom_script_tags_str
+        }
         ${
             use_bundled_gui
                 ? `<script>window.gui_env = 'prod';</script>`