Pass woocommerce coupon and payment processor (stripe, paypal, braintree, etc) via Drip Shopper API

The Drip Shopper API allows passing custom attributes in the payload (https://developer.drip.com/#sapi-create-or-update-order), these could be used to pass the WooCommerce coupon and payment processor used during orders. We can use this data to implement optimizations on our checkout pages and increase revenue.