feat: add OCP modes for kubelet credential provider integration

[porridge]

Summary

• Add OCP-GCR, OCP-ECR, OCP-ACR as supported modes for --use-kubelet-image-credential-integration, for OCP clusters on GCP, AWS, and Azure respectively.
• Each mode uses the corresponding cloud-specific credential provider config (gcr-credential-provider.yaml, ecr-credential-provider.yaml, acr-credential-provider.yaml) from /etc/kubernetes/credential-providers/ and binaries from /usr/libexec/kubelet-image-credential-provider-plugins, matching the paths used by the OpenShift machine-config-operator.

Test plan

• Deployed on an OCP/GCP cluster with OCP-GCR mode — volume mounts work, credential provider plugin initializes successfully (1 plugin loaded)

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/ocp-credential-provider

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