public long numConsumerGroups() {
        return consumerGroupGauges.values().stream()
            .mapToLong(timelineGaugeCounter -> timelineGaugeCounter.atomicLong.get()).sum();
    }
@return The total number of consumer groups.
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/metrics/GroupCoordinatorMetricsShard.java