code: @Reference(
              name = "carbon.metrics.service",
              service = MetricService.class,
              cardinality = ReferenceCardinality.MANDATORY,
              policy = ReferencePolicy.DYNAMIC,
              unbind = "unsetMetricService"
      )
      protected void setMetricService(MetricService metricService) {
          DataHolder.getInstance().setMetricService(metricService);
      }
docs: This bind method will be called when {@link MetricService} is registered.
  
  @param metricService The {@link MetricService} instance registered as an OSGi service