tools (xml_tools): implement `list-multi` in `_dataFormField2XMLUIData`: `list-multi` was missing and thus these data form field type was not supported, resulting in those fields shown as a text field. Due to legacy, current implementation use a hack to split values, this should be fixed later by using proper serialisation.

this certificates are used to enable TLS during tests. Those must be the same as in
backend_e2e (they are generated there)