ExitOnExtensionError will make Process return an error immediately if the pubsub extension/ acknowledgement process failed, without waiting for the callback to return its success/failure (i.e.

ExtensionPeriod is the duration by which to extend the ack deadline at a time.

NewConsumer returns a pubsub task queue client.

NewPublisher creates a pubsub publisher.

ReturnImmediately will return nil immediately if there are no messages to process.

Publisher implements messaging.Publisher.