systemd-resolved: use a drop-in for kubespray dns (#10732)

This avoid needlessly overriding things and make cleanup easier.
Also simplifies the template a bit.

roles/kubernetes/preinstall/tasks/0061-systemd-resolved.yml

@@ -1,8 +1,14 @@
 ---
-- name: Write resolved.conf
+- name: Create systemd-resolved drop-in directory
+  file:
+    state: directory
+    name: /etc/systemd/resolved.conf.d/
+    mode: 0755
+
+- name: Write Kubespray DNS settings to systemd-resolved
   template:
     src: resolved.conf.j2
-    dest: /etc/systemd/resolved.conf
+    dest: /etc/systemd/resolved.conf.d/kubespray.conf
     owner: root
     group: root
     mode: 0644