cache:flush command isn't supported

We deploy our TYPO3 v12 website via CI. After a successful deployment, we run the command cache:flush to clear caches and regenerate FE asset symlinks. This works as expected — the frontend cache is cleared, and the asset symlinks are correctly re-created. However, Varnish is not notified or invalidated by this command. As a result, outdated content may still be served from Varnish, even though new assets (e.g. updated CSS/JS files) are in place.

Can be introduced with this MR: !38 (merged)