PROTON-2893: [Python] Add callback for all delivery updates

This is useful for responding to delivery updates besides the common
AMQP updates. Specifically for better transaction support.

Author: astitcher

python/proton/_handlers.py

@@ -115,6 +115,7 @@ def on_delivery(self, event: DeliveryEvent):
                 self.on_rejected(event)
             elif dlv.remote_state == Delivery.RELEASED or dlv.remote_state == Delivery.MODIFIED:
                 self.on_released(event)
+            self.on_delivery_updated(event)
             if dlv.settled:
                 self.on_settled(event)
                 if self.auto_settle:
@@ -163,6 +164,18 @@ def on_released(self, event: DeliveryEvent):
         if self.delegate is not None:
             _dispatch(self.delegate, 'on_released', event)
 
+    def on_delivery_updated(self, event: DeliveryEvent):
+        """
+        Called when the remote peer updates the status of a delivery. Note that
+        this will be called even if the more specific disposition update events
+        are also called.
+
+        :param event: The underlying event object. Use this to obtain further
+            information on the event.
+        """
+        if self.delegate is not None:
+            _dispatch(self.delegate, 'on_delivery_updated', event)
+
     def on_settled(self, event: DeliveryEvent):
         """
         Called when the remote peer has settled the outgoing
@@ -917,6 +930,17 @@ def on_released(self, event: DeliveryEvent) -> None:
         """
         pass
 
+    def on_delivery_updated(self, event: DeliveryEvent) -> None:
+        """
+        Called when the remote peer updates the status of a delivery. Note that
+        this will be called even if the more specific disposition update events
+        are also called.
+
+        :param event: The underlying event object. Use this to obtain further
+            information on the event.
+        """
+        pass
+
     def on_settled(self, event: DeliveryEvent) -> None:
         """
         Called when the remote peer has settled the outgoing