Add a metric to the metric family.

        Args:
          labels: A list of label values
          value: A dict of string state names to booleans

def add_metric(self, labels, value, timestamp=None):
        """Add a metric to the metric family.

        Args:
          labels: A list of label values
          value: A dict of string state names to booleans
        """
        labels = tuple(labels)
        for state, enabled in sorted(value.items()):
            v = (1 if enabled else 0)
            self.samples.append(Sample(
                self.name,
                dict(zip(self._labelnames + (self.name,), labels + (state,))),
                v,
                timestamp,
            ))