[Feature] 期望增加 metric 可以对接 promtheus

### Description / 功能描述

支持 :8090/metrics

### Motivation / 请求动机

这样可以监控 certimate 服务状态以及相关数据

### Miscellaneous / 其他

_No response_

### Contribution / 贡献代码

- [x] I am interested in contributing a PR for this! / 我乐意为此提交代码并发起 PR！

The issue names a :8090/metrics endpoint but no files or tests. Start by locating the HTTP server entry point and checking how that port is configured; confirm which service metrics are expected, expose them at /metrics, and verify the endpoint and relevant tests.

Written by the indexing model from the issue text.