add tune example

Add a tune example usign Ax and Ray

ax with ray: https://ax.dev/tutorials/raytune_pytorch_cnn.html
mlflow with ax: https://github.com/mlflow/mlflow/tree/master/examples/pytorch/AxHyperOptimizationPTL

NAS
https://pytorch.org/blog/effective-multi-objective-nueral-architecture/

Start by reviewing the repository's existing examples and the linked Ax/Ray, MLflow/Ax, and NAS references. Add a tuning example that fits the tutorial structure and uses the requested approaches; done means the example is included and usable by following the project’s existing conventions.

Scritto dal modello di indicizzazione a partire dal testo della issue.