code: func (t *ImageCarouselTemplate) MarshalJSON() ([]byte, error) {
  	return json.Marshal(&struct {
  		Type    TemplateType           `json:"type"`
  		Columns []*ImageCarouselColumn `json:"columns"`
  	}{
  		Type:    TemplateTypeImageCarousel,
  		Columns: t.Columns,
  	})
  }
docs: // MarshalJSON method of ImageCarouselTemplate