Support zero hostnames in HTTPRoute

[pleshakov]

Describe the bug
NGINX Kubernetes Gateway doesn't try to attach to a listener if an HTTPRoute has 0 hostnames.

To Reproduce
Steps to reproduce the behavior:

Gateway -- https://github.com/nginxinc/nginx-kubernetes-gateway/blob/f74c06ded5c3d647b0909fe542f3e70dbc96774c/examples/cafe-example/gateway.yaml

HTTPRoute:

apiVersion: gateway.networking.k8s.io/v1beta1
kind: HTTPRoute
metadata:
  name: coffee
spec:
  parentRefs:
  - name: gateway
    sectionName: http
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /coffee
    backendRefs:
    - name: coffee
      port: 80

In the status of the HTTPRoute, NKG reports:

Status:
  Parents:
    Conditions:
      Last Transition Time:  2023-05-03T15:55:08Z
      Message:               Listener hostname does not match the HTTPRoute hostnames
      Observed Generation:   1
      Reason:                NoMatchingListenerHostname
      Status:                False
      Type:                  Accepted
    Controller Name:         k8s-gateway.nginx.org/nginx-gateway-controller
    Parent Ref:
      Group:         gateway.networking.k8s.io
      Kind:          Gateway
      Name:          gateway
      Namespace:     default
      Section Name:  http

Expected behavior

• HTTPRoute attaches to a listener
• Traffic (in this example) - curl <any-host>/coffee routes to coffee service

Additional context

Conformance tests often don't include hostnames in HTTPRoutes. Example -- https://github.com/kubernetes-sigs/gateway-api/blob/v0.6.2/conformance/tests/httproute-matching.yaml