Per ListenerSet frontend mTLS

Now I am in the process from migrating a cluster that relies heavily on Ingress-NGINX to NGINX Gateway fabric, and sadly it's a waste of precious time. And I say this as a a big NGINX fan.

Things that were super easy using Ingress-NGINX, appear to be cumbersome using the at best, or not possible at all with the Gateway API.

It is sad that Ingress-NGINX is already retired, because imho Gateway API is not ready to replace it yet.

**To the point:**

I would like to be able to scope MTLS per listenerSet. This would resemble my trusted ingress configuration more closely than the currently available options, gateway wide or per port.

Start by reading the Gateway API documentation and the existing mTLS configuration model, focusing on how listener sets and port-scoped settings are represented. Compare the current gateway-wide and per-port options with the requested per-listenerSet scope; done means the supported behavior and its API implications are specified.

Written by the indexing model from the issue text.