TODO: Move cache purging to a background queue instead of using middleware

[rafaucau]

Currently, the extension uses middleware to clear cache when resources are updated. This is the fastest and easiest solution, but there are problems when the resource is updated using a background queue or cron. It would be better to use events and run the cache purge command.
https://docs.flarum.org/extend/backend-events
https://api.flarum.org/php/v1.8.0/flarum/queue