Add cluster certificate and host outputs to the ske_cluster data

[tchelovilar]

Adding the cluster certificate and host outputs to the ske_cluster data will smoothly improve Kubernetes provider setup.

data "stackit_ske_cluster" "main" {
  project_id = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
  name       = "example-name"
}

provider "kubernetes" {
  host                   = data.stackit_ske_cluster.main.host
  cluster_ca_certificate = base64decode(data.stackit_ske_cluster.main.cluster_ca_certificate)

  exec {
    api_version = "client.authentication.k8s.io/v1"
    command     = "stackit"
    args        = ["ske", "kubeconfig", "login", "--project=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx", "--cluster=name"]
  }
}