Add `woocommerce_order_note_added` action

This action provides an easier way to perform an action when a non-customer order note is added.

includes/class-wc-order.php

@@ -1731,6 +1731,8 @@ class WC_Order extends WC_Abstract_Order {
 			);
 		}
 
+		do_action( 'woocommerce_order_note_added', $comment_id, $this );
+
 		return $comment_id;
 	}