const fields: IField[] = [
  {
    type: 'file', // required
    name: 'name-file', // require
    attributes: {
      id: 'id-field', // optional
      classes: ['form-control'], // optional
      label: 'Image', // optional
    },
    extra: {
      multiple: true, // optional
      showPreview: true // optional
    },
    rules: ['file'],
    file: { // need to add this attribute object if you need a file rule
      types: 'jpg,gif,png',
      maxsize: 5,
    },
  },
];