DimensionCacheConfig addOverride(MetricRule metricRule) {
      this.metricConfig.add(metricRule);
      return this;
    }
Add a MetricRule to be used to configure a custom TTL using the value from {@link
MetricRule#listMetricsCacheTtl} to override the default expiry

@param metricRule
@return this
src/main/java/io/prometheus/cloudwatch/CachingDimensionSource.java