'Add a metric to monitor an object that implements measurable.
This metric won\'t be associated with any sensor.
This is a way to expose existing values as metrics.
Arguments:
metricName (MetricName): The name of the metric
measurable (AbstractMeasurable): The measurable that will be
measured by this metric
config (MetricConfig, optional): The configuration to use when
measuring this measurable'

def add_metric(self, metric_name, measurable, config=None):

    metric = KafkaMetric(metric_name, measurable, (config or self.config))
    self.register_metric(metric)
