kube: always enable proxy protocol support (#5299)
kube: always enable proxy protocol support (#5299)

Proxy protocol is sometimes used by load balancers to communicate the
real client IP address. Re-use the detection/parsing code from
lib/multiplexer on all k8s listeners (proxy and kubernetes_service)
gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport