reset ssh connection to allow user changes to affect 'current login user'

Why:
Without this modification, we can't use docker with docker_users in same
playbook than the one which install docker.

How:
Check that docker_users are set and not in docker group before include
docker-users.yml. In docker-users.yml we call reset_connection from
ansible.builtin.meta collection after docker-users are added to docker
group.

Manual success tests:
* Try to install docker with only one user in docker-users and not in
  docker group => docker-users.yml include
* Try to install docker with only one user in docker-users but the user
  is in docker group => docker-users.yml not include
* Try to install docker with 2 users in docker-users, one user in docker
  group and the second not => docker-users.yml include
* Try to install docker with 2 users in docker-users, both are in docker
  group => docker-users.yml not include
* Try to install docker with 2 users in docker-users, both are not in
  docker group => docker-users.yml include

tasks/docker-users.yml

@@ -5,3 +5,7 @@
     groups: docker
     append: true
   with_items: "{{ docker_users }}"
+
+- name: Reset ssh connection to apply users changes
+  meta:
+    reset_connection

tasks/main.yml

@@ -79,5 +79,20 @@
 - include_tasks: docker-compose.yml
   when: docker_install_compose | bool
 
-- include_tasks: docker-users.yml
+- name: Get all docker group infos
+  getent:
+    database: group
+    key: docker
+    split: ':'
   when: docker_users | length > 0
+
+- name: Check there is at least one user to add to docker group
+  set_fact:
+    at_least_one_user_to_modify: true
+  when:
+    - docker_users | length > 0
+    - item not in ansible_facts.getent_group["docker"][2]
+  with_items: "{{ docker_users }}"
+
+- include_tasks: docker-users.yml
+  when: at_least_one_user_to_modify is defined