Add End-to-End Workflow Tutorial

What you would like to be added?

Create a tutorial in https://sdk.kubeflow.org/en/latest/ showing how all SDK clients work together in a complete ML workflow:

• Train a model with TrainerClient
• Optimize hyperparameters with OptimizerClient
• Register the best model with ModelRegistryClient

Why is this needed?

Currently, each client is documented in isolation. Users don't see how the pieces fit together or understand the intended workflow. A unified tutorial demonstrates the value of the SDK as a cohesive platform rather than separate tools.

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