Change the type of metrics(dubbo.provider.requests.xxx) to counter.

## Describe the proposal
En: Currently in the beta version of 3.2, the metric name (dubbo.provider.requests.total, dubbo.provider.requests.succeed, dubbo.provider.requests.failed) are all counter type, but they are displayed in the metrics panel The type of is: gauge, in order to prevent ambiguity, it needs to be changed to counter type.

中文：目前在3.2的beta版本中存在的监控指标埋点 (dubbo.provider.requests.total, dubbo.provider.requests.succeed, dubbo.provider.requests.failed) 均为 counter 类型，但是在 metrics 指标面板中显示的类型为：gauge，为了防止有歧义，需要修改为 counter 类型。