Refactor async execution handling across LDAP and Nextcloud roles

- Introduce global async configuration in group_vars/all/00_general.yml:
  - ASYNC_ENABLED (disabled in debug mode)
  - ASYNC_TIME (default 300s, omitted if async disabled)
  - ASYNC_POLL (0 for async fire-and-forget, 10 for sync mode)
- Replace hardcoded async/poll values with global vars in:
  - svc-db-openldap (03_users.yml, 04_update.yml)
  - web-app-mig (02_build_data.yml)
  - web-app-nextcloud (03_admin.yml, 04_system_config.yml, 05_plugin.yml,
    06_plugin_routines.yml, 07_plugin_enable_and_configure.yml)
- Guard changed_when and failed_when conditions to only evaluate in synchronous
  mode to avoid accessing undefined rc/stdout/stderr in async runs

  https://chatgpt.com/share/689cd8cc-7fbc-800f-bd06-a667561573bf

roles/web-app-nextcloud/tasks/07_plugin_enable_and_configure.yml

@@ -29,8 +29,11 @@
   when: plugin_vars_file.stat.exists
   register: config_set_shell
   changed_when: >
+    not ASYNC_ENABLED and
     (config_set_shell.stdout | default('')) is search(' set to ')
-  failed_when: config_set_shell.rc != 0
+  failed_when: not ASYNC_ENABLED and config_set_shell.rc != 0
+  async: "{{ ASYNC_TIME if ASYNC_ENABLED else omit }}"
+  poll:  "{{ ASYNC_POLL if ASYNC_ENABLED else omit }}"
 
 - name: Check if {{nextcloud_control_node_plugin_tasks_directory}}{{ plugin_key }}.yml exists
   stat: