Refactor async task handling

- Standardize async/poll usage with 'ASYNC_ENABLED | bool'
- Add async/poll parameters to Cloudflare, Nginx, Mailu, MIG, Nextcloud, and OpenLDAP tasks
- Update async configuration in 'group_vars/all/00_general.yml' to ensure boolean evaluation
- Allow CAA, cache, and DNS tasks to run asynchronously when enabled

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

roles/web-app-nextcloud/tasks/03_admin.yml

@@ -10,5 +10,5 @@
     ("is already a member of" not in (
       (add_admin_to_group.stderr | default('')) ~ (add_admin_to_group.stdout | default(''))
     ))
-  async: "{{ ASYNC_TIME if ASYNC_ENABLED else omit }}"
-  poll:  "{{ ASYNC_POLL if ASYNC_ENABLED else omit }}"
+  async: "{{ ASYNC_TIME if ASYNC_ENABLED | bool else omit }}"
+  poll:  "{{ ASYNC_POLL if ASYNC_ENABLED | bool else omit }}"