Performance issues in the program

[DLPerf]

Hello,I found a performance issue in aladdinpersson_Machine-Learning-Collection/ML/TensorFlow/Basics/tutorial7-indepth-functional.py , train_dataset.map was called without num_parallel_calls. I think it will increase the efficiency of your program if you add this.

The same issues also exist in test_dataset.map , ds_train = ds_train.map(read_image).map(augment).batch(2) and other three places.

Here is the documemtation of tensorflow to support this thing.

Looking forward to your reply. Btw, I am very glad to create a PR to fix it if you are too busy.