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/04_system_config.yml

@@ -14,6 +14,9 @@
     executable: /bin/bash
   register: syscfg_shell
   changed_when: >
+    not ASYNC_ENABLED and
     ( ((syscfg_shell.stdout | default('')) ~ (syscfg_shell.stderr | default(''))) 
       is search(' set to ') )
-  failed_when: syscfg_shell.rc != 0
+  failed_when: not ASYNC_ENABLED and syscfg_shell.rc != 0
+  async: "{{ ASYNC_TIME if ASYNC_ENABLED else omit }}"
+  poll:  "{{ ASYNC_POLL if ASYNC_ENABLED else omit }}"