🌐(frontend) remove hardcoded DINUM-specific URLs from support forms

Replace instance-specific URLs with configurable values to make the
application more generic and reusable for other deployments.

src/backend/meet/settings.py

@@ -330,6 +330,9 @@ class Base(Configuration):
         "use_proconnect_button": values.BooleanValue(
             False, environ_name="FRONTEND_USE_PROCONNECT_BUTTON", environ_prefix=None
         ),
+        "transcript": values.DictValue(
+            {}, environ_name="FRONTEND_TRANSCRIPT", environ_prefix=None
+        ),
     }
 
     # Mail