feat: Support creating separate PSC for each zone in GCP

[ciiiii]

Usage example

module "topology_aware_psc" {
  source = "git::https://github.com/streamnative/terraform-managed-cloud//modules/gcp/private-service?ref=main"

  domain_name  = "gcp-usc1-example.example.com"
  project      = "<your-client-gcp-project>"
  region       = "us-central1"
  network_name = "<your-client-network>"
  subnet_name  = "<your-client-subnet>"
  suffix       = "gcp-usc1-example"

  service_attachments = [
    {
      zone = "us-central1-a",
      id   = "projects/<pulsar-project>/regions/us-central1/serviceAttachments/istio-system-istio-ingressgateway-us-central1-a",
    },
    {
      zone = "us-central1-b",
      id   = "projects/<pulsar-project>/regions/us-central1/serviceAttachments/istio-system-istio-ingressgateway-us-central1-b",
    },
    {
      zone = "us-central1-c",
      id   = "projects/<pulsar-project>/regions/us-central1/serviceAttachments/istio-system-istio-ingressgateway-us-central1-c",
    }
  ]
}