Added PTQ section to BERT notebook

[svenchilton]

Description

Added a section on post-training quantization to the BERT notebook. This follows @peri044's fixes in https://github.com/pytorch/TensorRT/pull/1191 to allow support for post-training quantization with multiple inputs.

Fixes # (issue)

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code follows the style guidelines of this project (You can use the linters)
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas and hacks
• [ ] I have made corresponding changes to the documentation
• [ ] I have added tests to verify my fix or my feature
• [ ] New and existing unit tests pass locally with my changes
• [ ] I have added the relevant labels to my PR in so that relevant reviewers are notified

[svenchilton]

@narendasan, the github-actions bot says that some C++ code doesn't conform to the style guidelines and is requesting that I make some changes. I haven't touched the C++ code.

[svenchilton]

@peri044, the github-actions bot has once again requested that I make changes to some C++ code which it claims doesn't conform to the style guidelines. I haven't touched the C++ code.

[narendasan]

@peri044, the github-actions bot has once again requested that I make changes to some C++ code which it claims doesn't conform to the style guidelines. I haven't touched the C++ code.

Don't worry about it, it is talking about some standing issues that got checked in which will be resolved in an other PR

[github-actions[bot]]

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