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.

k3s/roles/agent-setup/defaults/main.yml

@@ -0,0 +1,3 @@
+dns_servers: 8.8.8.8 8.8.4.4
+network_config_path: /etc/systemd/network
+

k3s/roles/agent-setup/handlers/main.yml

@@ -0,0 +1,4 @@
+- name: Restart resolved
+  service:
+    name: systemd-resolved
+    state: restarted

k3s/roles/agent-setup/tasks/main.yml

@@ -0,0 +1,29 @@
+- name: Set default network route
+  shell: "ip route add default via {{ private_nat }}"
+  ignore_errors: "yes"
+  when: ansible_facts['default_ipv4']['alias'] is not defined
+
+- name: Regather facts
+  setup:
+  when: ansible_facts['default_ipv4']['alias'] is not defined
+
+- name: Gather fact target_nic
+  set_fact:
+    target_nic: "{{ ansible_facts['default_ipv4']['alias'] }}"
+
+- name: Ensure path to configure default route
+  file:
+    path: "{{ network_config_path }}"
+    state: directory
+
+- name: Configure default route
+  template:
+    src: nic.network.j2
+    dest: "{{ network_config_path }}/10-{{target_nic}}.network"
+
+- name: Configure DNS servers
+  lineinfile:
+    path: /etc/systemd/resolved.conf
+    regexp: '^#?\s*DNS\s*=.*'
+    line: "DNS={{ dns_servers }}"
+  notify: "Restart resolved"

k3s/roles/agent-setup/templates/nic.network.j2

@@ -0,0 +1,5 @@
+[Match]
+Name={{ target_nic }}
+[Network]
+DHCP=yes
+Gateway={{ private_nat }}