feat: fill in AttachedRoutes in Gateways' Listeners status

[pmalek]

What this PR does / why we need it:

This PR adds support for setting the correct attachedRoutes count in Gateway's listeners status.

Which issue this PR fixes

Part of #56

Special notes for your reviewer:

TestGatewayConformance/GatewayWithAttachedRoutes/Gateway_listener_should_have_AttachedRoutes_set_even_when_Gateway_has_unresolved_refs fails because for some reason HTTPRoute's status flips back and forth between

[
    {
        "parents": [
            {
                "conditions": [
                    {
                        "lastTransitionTime": "2024-05-09T12:16:14Z",
                        "message": "",
                        "observedGeneration": 1,
                        "reason": "Accepted",
                        "status": "True",
                        "type": "Accepted"
                    },
                    {
                        "lastTransitionTime": "2024-05-09T12:16:14Z",
                        "message": "",
                        "observedGeneration": 1,
                        "reason": "BackendNotFound",
                        "status": "False",
                        "type": "ResolvedRefs"
                    },
                    {
                        "lastTransitionTime": "2024-05-09T12:16:14Z",
                        "message": "",
                        "observedGeneration": 1,
                        "reason": "Unknown",
                        "status": "Unknown",
                        "type": "Programmed"
                    }
                ],
                "controllerName": "konghq.com/gateway-operator-integration-tests",
                "parentRef": {
                    "group": "gateway.networking.k8s.io",
                    "kind": "Gateway",
                    "name": "unresolved-gateway-with-one-attached-unresolved-route",
                    "namespace": "gateway-conformance-infra",
                    "sectionName": "tls"
                }
            }
        ]
    }
]

and

[
    {
        "parents": []
    }
]

Which I couldn't reproduce outside of conformance tests with manifests from https://github.com/kubernetes-sigs/gateway-api/blob/8b7639171b5ae5007c8a7abd1796f02a053313cf/conformance/tests/gateway-with-attached-routes.yaml#L90-L132

Below, I attach the dump of logs and resources as retrieved from the cluster during the conformance tests run. It seems that we do not set the ResolvedRefs condition on the Gateway properly when the tls secret that's referenced by the listener does not exist. That should be resolved separately when working on HTTPS/TLS routes

    helpers.go:716: 2024-05-21T18:56:23.89174+02:00: Programmed condition set to Status True with Reason Programmed, expected Status False
    helpers.go:716: 2024-05-21T18:56:23.891786+02:00: Programmed was not in conditions list [[{Conflicted False 1 2024-05-21 18:56:23 +0200 CEST NoConflicts } {Accepted True 1 2024-05-21 18:56:23 +0200 CEST Accepted } {Programmed True 1 2024-05-21 18:56:23 +0200 CEST Programmed } {ResolvedRefs False 1 2024-05-21 18:56:23 +0200 CEST InvalidCertificateRef Referenced secret gateway-conformance-infra/does-not-exist does not exist.}]]
    helpers.go:716: 2024-05-21T18:56:23.891848+02:00: Expected Conditions to be [{Programmed False 0 0001-01-01 00:00:00 +0000 UTC  } {ResolvedRefs False 0 0001-01-01 00:00:00 +0000 UTC  }], got [{Conflicted False 1 2024-05-21 18:56:23 +0200 CEST NoConflicts } {Accepted True 1 2024-05-21 18:56:23 +0200 CEST Accepted } {Programmed True 1 2024-05-21 18:56:23 +0200 CEST Programmed } {ResolvedRefs False 1 2024-05-21 18:56:23 +0200 CEST InvalidCertificateRef Referenced secret gateway-conformance-infra/does-not-exist does not exist.}]
    gateway-with-attached-routes.go:119:
                Error Trace:    /Users/patryk.malek@konghq.com/.gvm/pkgsets/go1.22.3/global/pkg/mod/sigs.k8s.io/gateway-api@v1.1.0/conformance/utils/kubernetes/helpers.go:718
                                                        /Users/patryk.malek@konghq.com/.gvm/pkgsets/go1.22.3/global/pkg/mod/sigs.k8s.io/gateway-api@v1.1.0/conformance/tests/gateway-with-attached-routes.go:119
                Error:          Received unexpected error:
                                error fetching Gateway: client rate limiter Wait returned an error: rate: Wait(n=1) would exceed context deadline
                Test:           TestGatewayConformance/GatewayWithAttachedRoutes/Gateway_listener_should_have_AttachedRoutes_set_even_when_Gateway_has_unresolved_refs
                Messages:       error waiting for Gateway status to have listeners matching expectations

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  creationTimestamp: "2024-05-21T17:34:45Z"
  generation: 1
  name: http-route-4
  namespace: gateway-conformance-infra
  resourceVersion: "416722"
  uid: 7041ffee-3393-4936-8a15-c72edfb3620a
spec:
  parentRefs:
  - group: gateway.networking.k8s.io
    kind: Gateway
    name: unresolved-gateway-with-one-attached-unresolved-route
    namespace: gateway-conformance-infra
    sectionName: tls
  rules:
  - backendRefs:
    - group: ""
      kind: Service
      name: does-not-exist
      port: 8080
      weight: 1
    matches:
    - path:
        type: PathPrefix
        value: /
status:
  parents: []
---
apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  creationTimestamp: "2024-05-21T17:34:45Z"
  finalizers:
  - gateway-operator.konghq.com/cleanup-controlplanes
  - gateway-operator.konghq.com/cleanup-dataplanes
  - gateway-operator.konghq.com/cleanup-network-policies
  generation: 1
  name: unresolved-gateway-with-one-attached-unresolved-route
  namespace: gateway-conformance-infra
  resourceVersion: "421522"
  uid: 4c7fa789-101e-4719-97fd-911d7ef4fd1f
spec:
  gatewayClassName: 2279a556-36e6-4fb5-a928-c67c0454263d
  listeners:
  - allowedRoutes:
      kinds:
      - group: gateway.networking.k8s.io
        kind: HTTPRoute
      namespaces:
        from: Selector
        selector:
          matchLabels:
            kubernetes.io/metadata.name: gateway-conformance-infra
    name: tls
    port: 443
    protocol: HTTPS
    tls:
      certificateRefs:
      - group: ""
        kind: Secret
        name: does-not-exist
      mode: Terminate
status:
  addresses:
  - type: IPAddress
    value: 172.18.128.6
  conditions:
  - lastTransitionTime: "2024-05-21T17:35:41Z"
    message: All listeners are accepted.
    observedGeneration: 1
    reason: Accepted
    status: "True"
    type: Accepted
  - lastTransitionTime: "2024-05-21T17:35:41Z"
    message: ""
    observedGeneration: 1
    reason: Programmed
    status: "True"
    type: Programmed
  - lastTransitionTime: "2024-05-21T17:35:41Z"
    message: ""
    observedGeneration: 1
    reason: Ready
    status: "True"
    type: DataPlaneReady
  - lastTransitionTime: "2024-05-21T17:35:41Z"
    message: ""
    observedGeneration: 1
    reason: Ready
    status: "True"
    type: ControlPlaneReady
  - lastTransitionTime: "2024-05-21T17:35:41Z"
    message: ""
    observedGeneration: 1
    reason: Ready
    status: "True"
    type: GatewayService
  listeners:
  - attachedRoutes: 1
    conditions:
    - lastTransitionTime: "2024-05-21T17:35:41Z"
      message: ""
      observedGeneration: 1
      reason: NoConflicts
      status: "False"
      type: Conflicted
    - lastTransitionTime: "2024-05-21T17:35:41Z"
      message: ""
      observedGeneration: 1
      reason: Accepted
      status: "True"
      type: Accepted
    - lastTransitionTime: "2024-05-21T17:35:41Z"
      message: ""
      observedGeneration: 1
      reason: Programmed
      status: "True"
      type: Programmed
    - lastTransitionTime: "2024-05-21T17:35:41Z"
      message: Referenced secret gateway-conformance-infra/does-not-exist does not
        exist.
      observedGeneration: 1
      reason: InvalidCertificateRef
      status: "False"
      type: ResolvedRefs
    name: tls
    supportedKinds:
    - group: gateway.networking.k8s.io
      kind: HTTPRoute

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect significant changes