List delivery attempts of a webhook event

Returns the delivery attempts that carried a specific webhook event, for each webhook endpoint subscribed to its event type. Endpoints receive events in ordered batches, so an attempt covers a batch (batchSize events) and is success, failed, pending or sending. eventId is either the event id (mwe_…, sent in every payload as webhookEventId) or the Svix message id (msg_…, the metadata.msg_id delivered with the event). complete is false when a webhook had more attempts than could be read: attempts may then be missing, so an empty list or a failed last attempt is not conclusive, and a listed success may lack some of its earlier failed attempts. With complete true, an empty list means no delivery was attempted yet.