GEP: Gateway API to Expose Pods on Cluster-Internal IP Address (ClusterIP)

[ptrivedi]

What would you like to be added:
We need to define via documentation how Gateway API can be used to accomplish ClusterIP Service behavior. As part of this definition, we want to

1. Propose DNS record format for ClusterIP Gateway
2. Propose an EndpointSelector resource to support Kubernetes resources besides Service (or external endpoints) directly as backendRefs
3. Briefly touch on Gateway API usage to define other types of Services like LoadBalancer and NodePort

Why this is needed:
Service API has become inflexible and bloated over time, and has posed some practical challenges. There have been discussions around Gateway API replacing or substituting for Service API. We ran into challenges when trying to support ClusterIP Services for multi-network pods, which were cleanly solved by Gateway API.