Description:
As a user I would like to enable and configure tcp keep-alive for 2 cases

• downstream with client
• upstream with server

here is the config needed in Envoy

• upstream
  https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/core/v3/address.proto#config-core-v3-tcpkeepalive

• downstream
  https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/core/v3/socket_option.proto#config-core-v3-socketoption

How other Envoy based implementations express this as an API

• Emissary has support https://www.getambassador.io/docs/emissary/latest/topics/using/keepalive#keepalive (unsure if this is downstream or upstream socket)
• Istio supports Upstream Keepalive https://istio.io/v1.1/docs/reference/config/networking/v1alpha3/destination-rule/#ConnectionPoolSettings-TCPSettings-TcpKeepalive
• Contour : TODO