Move configuration of servers completely to ansible

With this change we no longer use user-data scripts on the provided
machines. That makes it way easier for me to handle all the
configuration, since I only have to run ansible. Furthermore this the
burdon to think what may went wrong, since ansible is easier to debug
than some arbitrary scripts which run at provisioning-time on the
machines.

With this change I should also think about restructuring the code a bit
as well. Since it's actually easier to provide the initial
software-stack for the cluster via ansible than via terraform, at least
as far as I can tell right now.

infra/inventory.ini.tftpl

@@ -11,3 +11,7 @@ ${ip}
 [k3s_cluster:children]
 server
 agent
+
+[k3s_cluster:vars]
+network_cidr=${network_cidr}
+private_nat=${private_nat}