void bind(ThreadPoolExecutor pool) {
    Gauge.builder("zipkin_storage.throttle.concurrency", pool::getCorePoolSize)
      .description("number of threads running storage requests")
      .register(registryInstance);
    Gauge.builder("zipkin_storage.throttle.queue_size", pool.getQueue()::size)
      .description("number of items queued waiting for access to storage")
      .register(registryInstance);
  }
Follows the same naming convention as {@link MicrometerCollectorMetrics}
zipkin-server/src/main/java/zipkin2/server/internal/throttle/MicrometerThrottleMetrics.java