code: @VisibleForTesting
    protected void buildMetricsContextAndMetrics() {
      this.metricContext = Instrumented.getMetricContext(new org.apache.gobblin.configuration.State(ConfigUtils.configToProperties(config)),
          this.getClass(), getTagsForMetrics());
      createMetrics();
    }
docs: Called once on {@link #startUp()} to start metrics.