✨(project) add custom js support via config

From the config, we can add custom JS file URL
to be included in the frontend.

src/backend/impress/settings.py

@@ -509,6 +509,9 @@ class Base(Configuration):
     FRONTEND_CSS_URL = values.Value(
         None, environ_name="FRONTEND_CSS_URL", environ_prefix=None
     )
+    FRONTEND_JS_URL = values.Value(
+        None, environ_name="FRONTEND_JS_URL", environ_prefix=None
+    )
 
     THEME_CUSTOMIZATION_FILE_PATH = values.Value(
         os.path.join(BASE_DIR, "impress/configuration/theme/default.json"),