Introduce woocommerce_order_applied_coupon hook (#35616)

Co-authored-by: Néstor Soriano <konamiman@konamiman.com>
Closes https://github.com/woocommerce/woocommerce/issues/34473

plugins/woocommerce/changelog/34473-coupon-applied-to-order

@@ -0,0 +1,4 @@
+Significance: patch
+Type: add
+
+Add the woocommerce_order_applied_coupon hook

plugins/woocommerce/includes/abstracts/abstract-wc-order.php

@@ -1211,6 +1211,16 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 			}
 		}
 
+		/**
+		 * Action to signal that a coupon has been applied to an order.
+		 *
+		 * @param  WC_Coupon $coupon The applied coupon object.
+		 * @param  WC_Order  $order  The current order object.
+		 *
+		 * @since 7.3
+		 */
+		do_action( 'woocommerce_order_applied_coupon', $coupon, $this );
+
 		$this->set_coupon_discount_amounts( $discounts );
 		$this->save();