Data of an item group.
It is used for creating a SelectBox.
ItemGroup supports only 1 level choices, so it does not work to add item groups in the item group.
The example using item groups can be found here.

const itemGroupData = {
  label: 'disabled items',
  data: [
    { label: 'disable', value: 'disable' },
    { label: 'none', value: '0' }
  ],
  disabled: true
};