Adding evidence of performance improvement by using test-time augmentation (TTA) in the tutorial notebook

Current tutorial notebook about test-time augmentation (TTA) simply shows how to apply it for brain MRI segmentation in 2D planes. However, it is unclear the if the TTA method would improve the segmentation quality in practice.
https://github.com/Project-MONAI/tutorials/blob/master/modules/inverse_transforms_and_test_time_augmentations.ipynb

It is better to show the accuracy and quality (visual) improvement of segmentation masks and let users know how to properly apply the TTA method in practice boosting the performance.