Use Docker host alias for Kubernetes callbacks

[MarcStdt]

Summary

• use host.docker.internal for worker callbacks from k3d
• use the same host alias for the runtime MinIO endpoint

Validation

• make -n watch expands both host URLs correctly
• host.docker.internal resolves from a local k3d pod
• a local k3d pod reaches MinIO through the alias

[druid-infra]

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