Revisit Kubernetes Services mapping to Envoy v3.Cluster

[dprotaso]

Description:
I was surprised to see that Kubernetes services weren't mapped to envoy v3.Clusters. One thing I was hoping for was to create high level Gateway Policy resources that would then reconcile EnvoyPatchPolicy. I prefer not to build out an entire extension service.

I wanted my policy to target k8s services and then creating a patch could modify the v3.Cluster

Unfortunately, it seems like Gateway HTTPRoute backends maps to envoy v3.Clusters (which has it's own side effects #5230).

[guydc]

In general, I agree that in some cases it could be beneficial to map Backends/Services to a single cluster. For example, users may want to apply limits such as circuit breakers on a per-proxy-per-backend basis, and not have these limits duplicated per-route-backendref. Other issues include excessive active health checking from duplication of clusters and their HC settings, inconsistent passive health check status.