挑选折扣适用国家-DiscountShippingDestinationSelection union
选择此折扣适用的运输国家。
可能的类型
[DiscountCountries](https://shopify.dev/docs/admin-api/graphql/reference/discounts-and-marketing/discountcountries)
[DiscountCountryAll](https://shopify.dev/docs/admin-api/graphql/reference/discounts-and-marketing/discountcountryall)