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-max-retries
• x-envoy-retry-on
• x-envoy-upstream-rq-timeout-alt-response
• x-forwarded-client-cert
• x-forwarded-proto