Allow Flatpak utilities in Toolbox containers.

So the containers can access the host.

Ansible/roles/debian_server/tasks/toolbox.yml

@@ -46,10 +46,14 @@
         state: present
         update_cache: true
 
-- name: APT install Podman
+- name: APT install prerequisites
   apt:
     cache_valid_time: 3600
+    install_recommends: false
     name:
+      # Flatpak is needed for running flatpak-spawn inside the Toolbox
+      # containers.
+      - flatpak
       - podman
     state: present
     update_cache: true