stats: add emission rule for upstream_rq_active (#775)
stats: add emission rule for upstream_rq_active (#775)

Description: since traffic was moved to be able to select h2, upstream_rq_active is useful to determine concurrency.
Risk Level: low
Testing: CI

Signed-off-by: Jose Nino <ca94e32c82b10963d0ce6eadf427a615ff7d1c0b@lyft.com>
envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile,envoyproxy/envoy-mobile