use rq_total in load_stats_reporter to tell whether there is load

*Title*: use rq_total in load_stats_reporter to tell whether there is load

*Description*:
In load_stats_reporter.cc, Envoy use rq_active+rq_success+rq_error to tell whether there is load for a cluster locality.

See https://github.com/envoyproxy/envoy/pull/37083, in some rare cases, rq_total is a better indicator for load: no matter a response is received or not, a request is "handled"(activeStream, cluster picking, host picking, connection creation) by Envoy already.

We should just use rq_total to indicate whether there is load.

https://github.com/envoyproxy/envoy/blob/3a1a72e9d7a272e452bb5499c4dcdc43e1eee5ed/source/common/upstream/load_stats_reporter.cc#L106

[optional *Relevant Links*:]
>related total_issued introduced in https://github.com/envoyproxy/envoy/pull/6784