[Accessibility issue] Template variables: No designator for mandatory fields in forms (MAS issue: 258655)

**User experience** Low vision users and users with cognitive disabilities will face difficulty if there is no indicator for any required field. **Steps to reproduce**: Go to [play.grafana.org](https://play.grafana.org/). Navigate the Feature Showcase pane heading and select it. Navigate the expanded Dropdown and select the "Edit" menu item. Navigate the page "Edit Panel" page which appears. Navigate to "Settings" button and select it. Navigate the "Variables" tab item and select it. Navigate the "Variables" tab and "New" button. Navigate the "Variables edit" page. Navigate to 'Name and Query' edit fields. Verify the issue. **Actual Result**: There is no visual indicator what field is mandatory to be filled in. **Expected Result** There should be a visual indicator for required fields.