fix: Add higress-controller:8889 cluster for ACME challenge route

[CH3CHO]

The Let's Encrypt HTTPS certificate obtaining feature requires a temporary route pointing to higress-controller:8889 service for its HTTP-01 challenge.

https://github.com/higress-group/higress/blob/main/pkg/cert/ingress.go#L37

const (
	IngressClassName   = "higress"
	IngressServiceName = "higress-controller"
	IngressNamePefix   = "higress-http-solver-"
	IngressPathPrefix  = "/.well-known/acme-challenge/"
	IngressServicePort = 8889
)

Sample Virtual Service config:

{
  "apiVersion": "networking.istio.io/v1alpha3",
  "kind": "VirtualService",
  "metadata": {
    "annotations": {
      "internal.higress.io/cluster-id": ""
    },
    "name": "istio-autogenerated-k8s-ingress-higress-system-higress-http-solver-www-foo-com-3c4f64c1e7b5e505",
    "namespace": "higress-system"
  },
  "spec": {
    "gateways": [
      "higress-system/3c4f64c1e7b5e505",
      "istio-autogenerated-k8s-ingress-3c4f64c1e7b5e505"
    ],
    "hosts": [
      "www.foo.com"
    ],
    "http": [
      {
        "match": [
          {
            "uri": {
              "exact": "/.well-known/acme-challenge/_54X-6ScQXaRwuttmuVVUtFbeVB4UualX5DWw_pe4RQ"
            }
          },
          {
            "uri": {
              "prefix": "/.well-known/acme-challenge/_54X-6ScQXaRwuttmuVVUtFbeVB4UualX5DWw_pe4RQ/"
            }
          }
        ],
        "name": "higress-http-solver-www-foo-com",
        "route": [
          {
            "destination": {
              "host": "higress-controller.higress-system.svc.cluster.local",
              "port": {
                "number": 8889
              }
            },
            "weight": 100
          }
        ]
      }
    ]
  }
}

In standalone deployments, there is no K8s service discovery. So I just make it sample by creating the corresponding cluster using EnvoyFilter.

This PR fixes higress-group/higress#3789 .

[johnlanni]

LGTM