As a user, I want the apisix prometheus plugin to have a timer to clean all metrics, so as to ease the performance degradation problem when there are hundreds of thousands of metrics in prometheus.

[haoyang1994]

Description

I encountered a serious performance problem when using the apisix prometheus plugin. The reason for the problem was that we set too many metrics in prometheus. I saw that the community has done a lot of work for prometheus. But the expireTime feature seems to make metrics missing or inconsistent. I think it may be a feasible way to clean all prometheus metrics regularly. This method is similar to an apisix restart for the prometheus server. Of course, it is wrong to put too many indicators in prometheus, but I think regular cleaning will be a practical approach to ease the performance problem.