Optimize resources used in GatewayHTTPListenerIsolation

[arkodg]

What would you like to be added:

#3047 introduced the GatewayHTTPListenerIsolation test which deploys 2 YAML files

• https://github.com/kubernetes-sigs/gateway-api/blob/main/conformance/tests/gateway-http-listener-isolation-with-hostname-intersection.yaml
• https://github.com/kubernetes-sigs/gateway-api/blob/main/conformance/tests/gateway-http-listener-isolation.yaml

The resources used could be optimized to use one Gateway resource instead of 2, resulting in lesser infra resources (like Deployment & Service) provisioned in implementations reducing the cluster resource consumption in CI

Why this is needed:
Allowing implementations to run this test with lesser resource requirements