Fixes for Hetzner terraform and Hetzner Cloud (#8702)

* - add ability to specify the network_zone in hetzner terraform
- Export the network id from hetzner terraform the the generated inventory.ini

* - Add with_networks variable to allow different deployments of hcloud controller manager

- Add network id to hcloud controller secret (added via the inventory)

- Don't include extra_args if it's not set

contrib/terraform/hetzner/modules/kubernetes-cluster/output.tf

@@ -21,3 +21,7 @@ output "worker_ip_addresses" {
 output "cluster_private_network_cidr" {
   value = var.private_subnet_cidr
 }
+
+output "network_id" {
+  value = hcloud_network.kubernetes.id
+}