Support for sending metrics to Prometheus

[songoow]

Is your feature request related to a problem? Please describe.

目前Monitor 接口没有具体实现，无法获得程序运行时的监控指标

Describe the solution you'd like

type Monitor interface {

   OnEmitSessionMetrics(PerformanceMetrics, StabilityMetrics, ShareMemoryMetrics, *Session)

   Flush() error
}

实现 Monitor 接口，其中OnEmitSessionMetrics 方法发送metrics 到prometheus , Flush() 方法将metrics写到本地日志文件

Describe alternatives you've considered
不太确定用那种实现方式

1 在业务代码里面实现Monitor 接口，然后提供一个使用的example，放在example路径中
2 直接在shmipc-go 库里实现，对外提供接口的实现，写一个使用的example

Additional context

[songoow]

assign

[GuangmingLuo]

Thanks for your idea and PR contribution @liu-song . However, we won't proceed this until there is a specific user claim that they will use this feature in real scenario.