Corner Case: Clenup Processing for Delete Event Without Finalizer

If Cleaner interface is implemented by a reconciler a finalizer is automatically added to the custom resource, and cleaner is called before it gets removed.
There is however a corner case when it makes sense to do cleanup event finalizer is not used. In case there is an in memory data held for a custom resource, so when a custom resource deleted, related indexed or in memory objects needs to be cleaned up. In this case a finalizer is not needed, since if the operator is down and the delete event is missed it's not a problem, since the cleanup is just for in memory data.

To support this we could add a feature flag to @ControllerConfiguration to don't add finalizer for cleanup: addFinalizerForCleaner.

Note that this is not a priority issue, we should probably implement it only if some requests it. Also having a finalizer in those cases would not be a big issues.

@ControllerConfiguration アノテーションから始め、custom resource の削除時に Cleaner 実装が finalizer の処理をどのようにトリガーするかを追跡します。delete event がどこで処理され、cleanup がどのように呼び出されるかを確認します。提案された設定によって、cleanup の動作を変更せずに Cleaner が finalizer を追加するかどうかを制御でき、関連する動作がテストでカバーされていれば完了です。