Add example of group radios

  radios_options_grouped:
    '#type': radios
    '#title': radios_options_properties
    '#options_description_display': description
    '#options':
      one: 'One -- This is a description'
      two: 'Two -- This is a description'
      three: 'Three -- This is a description'
      four: 'Four -- This is a description'
    '#options__properties':
      one:
        '#prefix': '<h2>Group 1</h2>'
      three:
        '#prefix': '<h2>Group 2</h2>'