getLinkUrl method
Get amazon's product url.
Implementation
String getLinkUrl() {
var trackingId = setting.AmazonImageSetting().trackingId;
// https://www.amazon.co.jp/gp/product/B00N8JJCNQ?tag=flutter_amazon_image-22
return 'https://www.$domain/gp/product/$asin?tag=$trackingId';
}