Periodically send heartbeats.

def heartbeat(self):
        """Periodically send heartbeats."""
        while self._manager.is_active and not self._stop_event.is_set():
            self._manager.heartbeat()
            _LOGGER.debug("Sent heartbeat.")
            self._stop_event.wait(timeout=self._period)

        _LOGGER.info("%s exiting.", _HEARTBEAT_WORKER_NAME)