stats: add stats for specific 4xx codes (#902)
stats: add stats for specific 4xx codes (#902)

Description: add individual stats for some 4xx codes of interest at Lyft. In the future, like other stats we can have this be configurable.
Risk Level: low
Testing: local

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