add a new flax example for Bert model inference

[louie-tsai]

What does this PR do?

Add a new Flax inference example and show case how to optimize performance with Bfloat16 data types.
Most of the Flax examples are for Training/Fine Tuning, so it should be a good reference for inference

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

@ArthurZucker
@sanchit-gandhi
@stevhliu
@agramesh1
@mdfaijul

[stevhliu]

Thanks for adding a Flax example!

[stevhliu]

Thanks! Can you run make fixup or make style to fix the failing CI test (see step 5 here for more details)?

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[louie-tsai]

Thanks! Can you run make fixup or make style to fix the failing CI test (see step 5 here for more details)?
@stevhliu ran and fixed the issue accordingly. thanks

[stevhliu]

Thanks, docs look good to me! Pinging @ArthurZucker for a quick review since I'm not too familiar with Flax 😄