Make ssh-port of servers initially configurable

It looks somehow random that the SSH-port was simply defined in the
configuration of the k3s-setup. It looks somehow "configurable" although
it isn't. Therefore I moved this setting to the correct place in the
terraform-setup.

An important side-note is that this change doesn't make it possible to
_change_ the ssh-port, though. Once decided for an port and I have to
stick to it until I tear down the cluster!

infra/modules/hetzner/kubernetes/variables.tf

@@ -42,3 +42,8 @@ variable "ssh_exposed_ips" {
   type = list(string)
   default = []
 }
+
+variable "ssh_port" {
+  type = number
+  default = 1022
+}