fix(aws-lambda) report upstream latency
fix(aws-lambda) report upstream latency

No headers/tokens are injected but the plugin now reports the
time spent for the upstream Lambda request as KONG_WAITING_TIME,
which in turn shows up in the logs as 'latency.proxy'.

Note: the reported 'kong' latency is still of, but this is non
influencable from a plugin

Kong/kong,Kong/kong,Kong/kong