[AL-1724] tobytes for Pytorch & Tensorflow

[farizrahman4u]

🚀 🚀 Pull Request

Checklist:

• My code follows the style guidelines of this project and the Contributing document
• I have commented my code, particularly in hard-to-understand areas
• I have kept the coverage-rate up
• I have performed a self-review of my own code and resolved any problems
• I have checked to ensure there aren't any other open Pull Requests for the same change
• I have described and made corresponding changes to the relevant documentation
• New and existing unit tests pass locally with my changes

Changes

ds.pytorch(tobytes=True)   # all tensors return samples as bytes during iteration
ds.pytorch(tobytes=["x", "y"])  # specified tensors return samples as bytes during iteration