orderingKey property
If non-empty, identifies related messages for which publish order should be respected.
If a Subscription has enable_message_ordering set to true, messages
published with the same non-empty ordering_key value will be delivered
to subscribers in the order in which they are received by the Pub/Sub
system. All PubsubMessages published in a given PublishRequest must
specify the same ordering_key value. For more information, see
ordering messages.
Optional.
Implementation
core.String? orderingKey;