[MGMTXP] Fix tooltip text in Jira connector (#182358)

## Summary

Fixed an inconsistency in the tooltip helper text for the Jira connector
`Additional fields` field.

**before**
![Screenshot 2024-04-30 at 14 35
50](https://github.com/elastic/kibana/assets/1533137/c89d7ad2-0c54-46c3-8e81-89fd2144a89c)

**after**
<img width="377" alt="Screenshot 2024-05-02 at 14 22 46"
src="https://github.com/elastic/kibana/assets/1533137/2b15d65b-9ddb-42a8-bc49-9265d977e981">

x-pack/plugins/stack_connectors/public/connector_types/jira/jira_params.tsx

@@ -417,7 +417,7 @@ const JiraParamsFields: React.FunctionComponent<ActionParamsProps<JiraActionPara
                     'xpack.stackConnectors.components.jira.otherFieldsHelpText',
                     {
                       defaultMessage:
-                        'Custom fields are not validated by the connector. To avoid failed actions, ensure compliance with your Jira policies.',
+                        'Additional fields are not validated by the connector. To avoid failed actions, ensure compliance with your Jira policies.',
                     }
                   )}
                 />