enableExactlyOnceDelivery

If true, Pub/Sub provides the following guarantees for the delivery of a message with a given value of message_id on this subscription: * The message sent to a subscriber is guaranteed not to be resent before the message's acknowledgement deadline expires. * An acknowledged message will not be resent to a subscriber. Note that subscribers may still receive multiple copies of a message when enable_exactly_once_delivery is true if the message was published multiple times by a publisher client. These copies are considered distinct by Pub/Sub and have distinct message_id values.