Enable API Server VNET Integration

[zioproto]

https://learn.microsoft.com/en-us/azure/aks/api-server-vnet-integration
closes #13

[nellyk]

looks like it is failing because of this

│ "message": "Feature Microsoft.ContainerService/EnableAPIServerVnetIntegrationPreview is not enabled. Please see https://aka.ms/aks/previews for how to enable features.",

[kewalaka]

This is possible, noting it is a preview service:

resource "azapi_update_resource" "aks_api_server_access_profile" {
  type = "Microsoft.ContainerService/managedClusters@2024-09-02-preview"
  body = {
    properties = {
      apiServerAccessProfile = {
        enableVnetIntegration = var.api_server_vnet_integration #true
      }
    }
  }
  resource_id = azurerm_kubernetes_cluster.this.id
}

& because it is in preview the variable needs decorating like this to align to AVM spec requirements (& confirmation from the PG, I believe) :

variable "api_server_vnet_integration" {
  type        = bool
  default     = false
  description = <<DESCRIPTION
  # https://azure.github.io/Azure-Verified-Modules/specs/shared/#id-sfr1---category-composition---preview-services
  THIS IS A VARIABLE USED FOR A PREVIEW SERVICE/FEATURE, MICROSOFT MAY NOT PROVIDE SUPPORT FOR THIS, PLEASE CHECK THE PRODUCT DOCS FOR CLARIFICATION

  Enable VNET integration for the AKS cluster

  This requires the following preview feature registered on the subscription:

  az feature register --namespace "Microsoft.ContainerService" --name "EnableAPIServerVnetIntegrationPreview"
DESCRIPTION
}

[zioproto]

@kewalaka the problem is that the subscription where our CI is running does not have preview features registered.