HTTP header sanitizing

Envoy will potentially sanitize the following headers:

• x-envoy-decorator-operation
• x-envoy-downstream-service-node
• x-envoy-external-address
• x-envoy-ip-tags
• x-envoy-retry-grpc-on
• x-envoy-upstream-rq-per-try-timeout-ms
• x-envoy-upstream-rq-timeout-ms
• x-forwarded-for