Gets a product's available variants based on the specified product ID and either option choices or variant IDs.
The getProductVariants() function returns a Promise that is resolved
to an array of VariantItem objects when the product variants with the specified
choices or variant IDs are retrieved.
ID of the product whose variants are being retrieved. Pass only this field to retrieve all of the specified product's variants.
Variant options to return. If not specified, all the product's variants are returned.