feat: add worker nodes to docker swarm setup

roles/common/meta/argument_specs.yml

@@ -9,6 +9,7 @@ argument_specs:
         type: "list"
         elements: "str"
         required: false
+        default: []
         description:
           - "Additional groups that will be added to each user"
       robo_allowed_commands:

roles/common/tasks/main.yaml

@@ -1,10 +1,5 @@
 # yaml-language-server: $schema=https://raw.githubusercontent.com/ansible/ansible-lint/refs/heads/main/src/ansiblelint/schemas/tasks.json
 
-- name: Create a user group named docker
-  loop: "{{ extra_groups }}"
-  ansible.builtin.group:
-    name: "{{ item }}"
-
 - name: Setup users
   loop: "{{ users }}"
   ansible.builtin.user:
@@ -14,7 +9,7 @@
     shell: "{{ item.shell }}"
     create_home: true
     password: "{{ (item.password != '!' or item.password != '*') | ternary(item.password | password_hash('sha512'), item.password) }}"
-    groups: "{{ item.groups + extra_groups }}"
+    groups: "{{ item.groups + (extra_groups | default([])) }}"
 
 - name: Add SSH public key to users
   loop: "{{ users }}"