SW-957: by default, expire message after 5 days

LCS/Messaging/python/messaging/messages.py

@@ -74,10 +74,10 @@ class LofarMessage:
                                       'Subject': self.subject}
                           }
 
-        if self.ttl:
+        if self.ttl is not None:
             # https://www.rabbitmq.com/ttl.html#per-message-ttl-in-publishers
-            # Since the expiration field must be a string, the broker will (only) accept the string representation of the number.
-            publish_kwargs['expiration'] = str(self.ttl)
+            # https://docs.celeryq.dev/projects/kombu/en/stable/reference/kombu.html?highlight=publish#kombu.Producer.publish
+            publish_kwargs['expiration'] = float(self.ttl)
 
         return publish_kwargs