Adding tags to a span with Kamon OpenTracing support

AddDefaultTags.scala

  private lazy val cachedEnv = sys.env
  
  def addDefaultTags(builder: SpanBuilder) = {
    builder.withSpanTag("class", getClass().getName)

    cachedEnv.get("KUBERNETES_POD").foreach { pod =>
      builder.withSpanTag("kubernetes.pod", pod)
    }
    cachedEnv.get("KUBERNETES_NAMESPACE").foreach { namespace =>
      builder.withSpanTag("kubernetes.namespace", namespace)
    }
    cachedEnv.get("KUBERNETES_NODE").foreach { node =>
      builder.withSpanTag("kubernetes.node", node)
    }
    builder
  }