public <T> void addImmutableValueMetric(MetricNameTemplate nameTemplate, final T value) {
            MetricName metricName = metricName(nameTemplate);
            metrics().addMetricIfAbsent(metricName, null, (Gauge<T>) (config, now) -> value);
        }
Add to this group an indicator metric that always returns the specified value.

@param nameTemplate the name template for the metric; may not be null
@param value        the value; may not be null
@throws IllegalArgumentException if the name is not valid
connect/runtime/src/main/java/org/apache/kafka/connect/runtime/ConnectMetrics.java