Add new conversion tracking tag (coupon code)

For affiliate type systems it would be helpful to add a tag that can output the used coupon code on the order complete page. Some affiliate systems can use this to track and reward affiliates. For example, you may have an affiliate on instagram/tiktok that promotes your products using a coupon code. If there was a tag to output the code on the order complete page affiliate systems can then automate rewarding your affiliate.