[WIP]feat: Support shared vpc in GCP vendor access module

[ciiiii]

module "sn_managed_cloud_shared_vpc" {
  source          = "github.com/streamnative/terraform-managed-cloud//modules/gcp/vendor-access?ref=v3.8.0"
  project         = "<YOUR_PROJECT>"
  project_num     = "<YOUR_PROJECT_NUM>"
  network_project = "<YOUR_NETWORK_HOST_PROJECT>"
  shared_vpc_subnets = [{
    name   = "<SHARED_SUBNET_NAME>"
    region = "<SHARED_SUBNET_REGION>"
  }]
}