docker2podman: do not hardcode group name

let's use `client_group_name` instead of hardcoding the name.

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit 7fe0d55eff)

infrastructure-playbooks/docker-to-podman.yml

@@ -33,7 +33,7 @@
       setup:
       delegate_to: "{{ item }}"
       delegate_facts: True
-      with_items: "{{ groups['all'] | difference(groups.get('clients', [])) }}"
+      with_items: "{{ groups['all'] | difference(groups.get(client_group_name | default('clients'), [])) }}"
       run_once: true
       when: delegate_facts_host | bool