publishIdChangeToSubscribers = (id, payload) => {
      const idTopic = idsToTopics.get(id);
      if (idTopic !== undefined) {
        idTopic.publisher.next(payload);
      }
    }
Publishes an id change to its subscribers, if any.

@param {string} id - The id to publish a change for.
@param {PetStoreIdNameChange} payload - The payload to publish.