Add --override-manager flag for server-side apply drift detection

[yozel]

This flag allows specifying field managers whose ownership should be transferred to the helm-controller before performing drift detection. When a disallowed field manager is detected on a managed resource, its field ownership is replaced with the helm-controller's field owner, enabling proper drift detection for fields that were previously modified by other controllers or tools (e.g., kubectl).

This feature mirrors the --override-manager flag available in FluxCD's kustomize-controller, providing consistent behavior across Flux components for managing server-side apply field ownership conflicts.

Since it doesn't change the default behavior, the implementation doesn't introduce any breaking changes.

Fix: https://github.com/fluxcd/helm-controller/issues/896