main: Install qemu-guest-agent on proxmox VMs

proxmox UI can show more VM specific information if qemu-guest-agent is
installed in guest VMs.

main.yml

@@ -35,6 +35,16 @@
       include_role:
         name: users
 
+- hosts: proxmox
+  become: true
+
+  tasks:
+
+    - name: Ensure qemu guest agent is installed on proxmox VMs
+      ansible.builtin.apt:
+        pkg: qemu-guest-agent
+        state: present
+
 - name: Tau specific setup
   import_playbook: tau.yml