service as Route parentRefs

*Description*:
> Does envoy-gateway support Routes where the parentRefs refere to a kubernetes service -
If not - can it be supported ?
example from a cilium-gateway httpRoute:

```
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
name: nginx-route-1
spec:
parentRefs:
- group: ""
kind: Service
name: gamma-nginx
port: 80
```
In this context, there is no need to even create a Gateway resource.

I know it's possible to setup a ClusterIP service using the envoyConfig options - instead of the default LoadBalancer,
but you still have to wait for the controller to create that service and the name is not flexible,
where if the HttpRuote allowed an existing service for parent - then it's easier to manage - without any Gateway.

[optional *Relevant Links*:]
>Any extra documentation required to understand the issue.