ref(roles): All roles use desired package state

By setting the `desired_package_state` variable we can change if ansible
should only ensure that the packages exist on the system (`present`) or
that they are also updated to their latest version (`latest`).

roles/display_manager/tasks/main.yaml

@@ -2,14 +2,14 @@
 - name: Ensure user group for greeter exists
   ansible.builtin.group:
     name: "{{ greeter_user }}"
-    state: present
+    state: "present"
 
 - name: Install greetd and tuigreet
   community.general.xbps:
     name:
       - greetd
       - tuigreet
-    state: present
+    state: "{{ desired_package_state | default('present') }}"
   tags:
     - packages