Refactor ResticRepositoryEnsurer controller with kubebuilder

[blackpiglet]

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A sub task of epic #2597 to refactor ResticRepositoryEnsurer controller with kubebuilder.

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Environment:

• Velero version (use velero version):
• Kubernetes version (use kubectl version):
• Kubernetes installer & version:
• Cloud provider or hardware configuration:
• OS (e.g. from /etc/os-release):

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[reasonerjt]

@Lyndon-Li
The Ensurer is not really controller but a utility. What we need is just replace the client to use the one from controller-runtime.

[Lyndon-Li]

Fixed by #5308