[ISSUE #3456]🚀Add PopMetricsConstant struct and organized metrics for RocketMQ Pop operations✨ (#3457)

Author: mxsm

rocketmq-broker/src/metrics.rs

@@ -16,3 +16,4 @@
  */
 pub(crate) mod broker_metrics_constant;
 pub(crate) mod consumer_attr;
+pub(crate) mod pop_metrics_constant;