Allow Consul API Gateway controller to read ReferencePolicy

[nathancoleman]

This is a prerequisite for hashicorp/consul-api-gateway#142 being included in a release.

Changes proposed in this PR:
Allow the Consul API Gateway controller to get, list and watch ReferencePolicy from the k8s Gateway API. This will allow the controller to verify that a route is allowed to send traffic to a service in a different namespace.

In this example, the ReferencePolicy allows any HTTPRoute in the gateway-conformance-infra namespace to attach to the web-backend service in the gateway-conformance-web-backend namespace. Without this policy, cross-namespace routing will be blocked at some point in the future.

apiVersion: gateway.networking.k8s.io/v1alpha2
kind: ReferencePolicy
metadata:
  name: reference-policy
  namespace: gateway-conformance-web-backend
spec:
  from:
    - group: gateway.networking.k8s.io
      kind: HTTPRoute
      namespace: gateway-conformance-infra
  to:
    - group: ""
      kind: Service
      name: web-backend

How I've tested this PR:
Consumed in our conformance testing Actions workflow here

How I expect reviewers to test this PR:

Checklist:

• Tests added
• CHANGELOG entry added

  HashiCorp engineers only, community PRs should not add a changelog entry.
  Entries should use present tense (e.g. Add support for...)