Better transformer HF example

[HamidShojanazeri]

Description

This PR will add the Better Transformer optimization to the current HF example. This optimization does not change anything in the model just map the layer names from HF to match expected names in NN.Transformer module where we have faster kernels.

Also, need to mention that the optimized model can not be saved for now, it is numerically stable meaning there is no accuracy degradation after the changes.

Fixes #(issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ x] New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Feature/Issue validation/testing

This requires PT 1.13, will upload the regression test logs.

• Test A
  Logs for Test A

• Test B
  Logs for Test B

[codecov]

Codecov Report

Merging #2002 (52998b2) into master (8d877b0) will not change coverage.
The diff coverage is n/a.

❗ Current head 52998b2 differs from pull request most recent head b794b7c. Consider uploading reports for the commit b794b7c to get more accurate results

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[msaroufim]

Looks good, left some minor nits. Also please run the lint and spellchecking jobs before checking this in

[msaroufim]

we can remove this

[msaroufim]

Assuming all CI is green we're good to go