zoph: Hide configuration form when app is disabled

- MySQL server may be disabled when zoph is disabled. Trying to retrieve
configuration or trying to set the configuration at the time will result in
failures. So, disable the configuration form so that get/set of configuration
does not happen.

Tests:

- Disable zoph. Configuration form will disappear. Re-enable zoph, configuration
form will reappear.

- Functional tests for zoph pass.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/zoph/__init__.py

@@ -46,6 +46,8 @@ class ZophApp(app_module.App):
 
     _version = 2
 
+    configure_when_disabled = False
+
     def __init__(self) -> None:
         """Create components for the app."""
         super().__init__()