feat(nfs): Restrict server to v4 by default

Can be changed with `nfs_v4_only=false` which defaults to true.

Information taken from: https://wiki.debian.org/NFSServerSetup
and applied directly through Ansible.

Currently _irreversible_, meaning once we set the server to v4 only
there is NO ansible-supported playbook to reset it to all NFSv2/3/4
versions.

Has to be done manually, or could be included as manually-run playbook.

roles/nfs/tasks/main.yaml

@@ -10,7 +10,7 @@
   ansible.builtin.template:
     src: exports.jinja
     dest: /etc/exports
-    mode: '0644'
+    mode: "0644"
   become: true
   notify: Reload nfs service
 
@@ -22,6 +22,10 @@
   become: true
   loop: "{{ nfs_export_lines }}"
 
+- name: Disable NFSv2/NFSv3 to leave NFSv4-only server
+  ansible.builtin.include_tasks: "nfs-v4-only.yaml"
+  when: "nfs_v4_only"
+
 - name: Enable nfs server unit
   ansible.builtin.systemd:
     enabled: true