Merge infra and k3 into one directory again

Since I don't have multiple terraform steps anymore it simply doesn't
make sense to me anymore to split all tasks into separate folders.
Instead I try to be as clear as possible in the README to make it easy
to follow the structure in the future without too much headache.

roles/server-setup/defaults/main.yml

@@ -0,0 +1,2 @@
+ip_masquerade_path: /etc/networkd-dispatcher/routable.d
+ip_masquerade_script: 10-eth0-post-up