add cancel

proto/checkout.proto

@@ -95,6 +95,12 @@ message ContactDetailsUpdated  {
     optional string name = 3;
 }
 
+message CancelPayment {
+    string paymentId = 1;
+    optional string reason = 2;
+    google.protobuf.Timestamp cancelledAt = 3;
+}
+
 message InventoryReserved  {
     string id = 1;
     string status = 2;