fix: allow grpcs and tls for client_certificate

[shaneutt]

Summary

A discussion in kong/kubernetes-ingress-controller wherein a user was trying to use mTLS with gRPC indicated a bug in the Kong Gateway where grpcs wasn't allowed to have a client_certificate, this PR attempts to fix that (and also add tls while we're at it for similar reasons).

Full changelog

• Fixed a bug where grpcs and tls could not be used with client_certificate in services

Issue reference

Fix for https://github.com/Kong/kubernetes-ingress-controller/discussions/2831

[shaneutt]

I could use some help in verifying this solution according to the problem that was seen in https://github.com/Kong/kubernetes-ingress-controller/discussions/2831.

[shaneutt]

Thanks @flrgh :+1:

I'm going to temporarily close this, as in the time since I originally made this PR I've changed teams. The intention right now is that someone from my previous team will be picking this back up in the future.