Add request_id to instance action notifications

As it was agreed on the Rocky PTG [1] it is useful to have the
request_id of in the payload of every instance action versioned
notification. For example it could help the deployer connect
the state change described in the notification with the user
action, the request, on the REST API.

So this patch proposes to extend the InstanceActionPayload
versioned object with a new request_id field and populate
the request_id from the context object used for emitting
the instance action notifications.

[1] https://etherpad.openstack.org/p/nova-ptg-rocky L391

Implements: bp add-request-id-to-instance-action-notifications

Change-Id: I7243b60938d6e9c7c2bc2aacdba5c667cca8ec9b

doc/notification_samples/common_payloads/InstanceActionVolumeSwapPayload.json

@@ -6,5 +6,5 @@
     },
     "nova_object.name": "InstanceActionVolumeSwapPayload",
     "nova_object.namespace": "nova",
-    "nova_object.version": "1.5"
+    "nova_object.version": "1.6"
 }