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/main.tf

@@ -6,7 +6,7 @@ resource "hcloud_network" "kubernetes" {
 resource "hcloud_network_subnet" "kubernetes" {
   type         = "cloud"
   network_id   = hcloud_network.kubernetes.id
-  network_zone = "eu-central"
+  network_zone = var.network_zone
   ip_range     = var.private_subnet_cidr
 }