refactor(k3s): centralize k3s primary server IP and integrate Netcup DNS

Signed-off-by: Tuan-Dat Tran <tuan-dat.tran@tudattr.dev>

vars/group_vars/all/vars.yml

@@ -18,3 +18,7 @@ internal_domain: "seyshiro.de"
 #
 
 arch: "{{ 'arm64' if ansible_architecture == 'aarch64' else 'amd64' }}"
+
+netcup_api_key: "{{ vault_netcup.api_key }}"
+netcup_api_password: "{{ vault_netcup.api_password }}"
+netcup_customer_id: "{{ vault_netcup.customer_id }}"