generate_classification_report() does not show plot

In the first lab (SageMaker XGBoost HPO.ipynb), [generate_classification_report()](https://github.com/aws-samples/sagemaker-101-workshop/blob/d49b827f647c9f050879ca60e81afc890d0e7a22/builtin_algorithm_hpo_tabular/util/classification_report.py#L168) is called a couple of times. There does not appear to be a final call to `plt.show()` (from matplotlib.pyplot), and so the report does not display in the notebook.

Adding the lines `import matplotlib.pyplot as plt` and `plt.show()` to the notebook solves the issue, but `plt.show()` should probably be added to the utility function itself.

Start in builtin_algorithm_hpo_tabular/util/classification_report.py around line 168 and inspect how generate_classification_report() is called from SageMaker XGBoost HPO.ipynb. Verify the report's plotting behavior in the first lab, then confirm the notebook displays the generated report without requiring an extra plotting call.

Written by the indexing model from the issue text.