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

group_vars/all/06_nginx.yml

@@ -23,4 +23,5 @@ nginx:
     cache:
       general:        "/tmp/cache_nginx_general/"           # Directory which nginx uses to cache general data
       image:          "/tmp/cache_nginx_image/"             # Directory which nginx uses to cache images
-  user:               "http"                                # Default nginx user in ArchLinux
+  user:               "http"                                # Default nginx user in ArchLinux
+