Implement methods to cluster URL into low-cardinality

[dxsup]

Some users reported that the metrics kindling_entity_request_xxx contains a high-cardinality label request_content when the protocol is http. In this case, request_content represents the URL without parameters of the HTTP requests.

Since the URL could be changed a lot, there will be a mount of timeseries stored in the kindling-collector and these metrics will cause a lot of load on the memory of it and Prometheus. We should work around this issue to improve the stability of Kindling.

[dxsup]

Closed by #268