Add batch size of map function in the preprocessed dataset

[naem1023]

What does this PR do?

Add batch size arguments for map function in the _get_preprocessed_dataset.

• Some of machine can't accept the default batch size(1000) of dataset map function.
• Therefore, users should be able to modify the batch size of the map function through external arguments.

Before submitting

• Did you read the contributor guideline?
• Did you write any new necessary tests?

[hiyouga]

LGTM