Update the model training walkthrough tutorial to use Epochs instead of TensorFlow.Datasets

[BradLarson]

The model training walkthrough tutorial notebook uses the Iris CSV-based dataset in its example code. The implementation of this relies on the old TensorFlow.Dataset API, which has been deprecated in favor of the new Epochs API.

This notebook (and supporting code file) should be updated to use the new Epochs API to parse the Iris dataset and perform training.