Proposal: support prometheus metric export

[Zheaoli]

For now, in some circumstances, the cnpmcore has been one of the core dependencies in a company.

So it's too important to make this server more reliable. There would be great to export metrics to help the team to monitor the server status.

For now, Prometheus is the most popular monitoring platform in the world, and the node has supported the Prometheus SDK. FYI https://github.com/siimon/prom-client

So I think we can support the metric export in Prometheus and support some official grafana monitor dashboards.

This is just an idea, I will update more design detail when the maintainer think this idea is reasonable and workable.

[github-actions]

我们已经看到你的反馈，如果是功能缺陷，可以提供一下重现该问题的方式；如果是新功能需求，我们会尽快加入讨论。同时我们非常期待你可以加入我们的贡献者行列，让项目可以长期可持续发展。

[fengmk2]

pr is welcome

[imharyohm]

Can you please explain me what to resolve in this issue ?