Add support for for verifying client certs

[Stevenjin8]

See https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/annotations/#client-certificate-authentication.

Unfortuantely, some features like checking cn is not available in GW api: https://gateway-api.sigs.k8s.io/reference/1.4/spec/#frontendtlsvalidation