Li Shenzhi

完善sms的返回error的信息

1

不清楚会不会影响其他代码，麻烦您给看看。

help request: How to expose custom Prometheus metric with custom plugin

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### Description How to expose a metric from custom plugin, using the default prometheus exported URI `/apisix/prometheus/metrics`. In my case, I want get summary metric about request_time, not the builtin...