Implement finalizers in a Kubernetes operator for clean external resource deletion

Steps

1. Define a finalizer constant string in your controller (e.g., `myapp.example.com/finalizer`)
2. In the reconcile loop, check `object.DeletionTimestamp.IsZero()` to distinguish active from deleting objects
3. If not deleting and finalizer absent, add it with `controllerutil.AddFinalizer` and update the object
4. If deleting and finalizer present, run cleanup logic (e.g., delete external cloud resource), then call `controllerutil.RemoveFinalizer` and update
5. Return after adding or removing the finalizer; do not proceed with normal reconciliation in the same loop iteration