Enhance: prometheus metric filter

[Alanxtl]

现在指标上报有两个插件 dgp.filter.http.metric 和 dgp.filter.http.prometheusmetric

#573 have discussed the duplication of dgp.filter.http.metric and dgp.filter.http.prometheusmetric

这两个插件一个对应的是推模式一个对应的是拉模式

应该增强指标上报的能力:

• enhance the ability of dgp.filter.http.metric (currently the metrics need to be exported are hardcoded, we can implement a registry mechanism, everywhere in pixiu can register metrics (metric provider), and dgp.filter.http.metric export all the metrics (metric consumer))

[Alanxtl]

@jintao

[KamToHung]

@jintao

Please assigned to me