Extend Script to enable conversion of Encoder Only  T5x Models to Pytorch
Author: ToluClassics
Pull request: yes

# What does this PR do?

This PR Extends the [Script that converts T5x Models to Pytorch](https://github.com/huggingface/transformers/blob/main/src/transformers/models/t5/convert_t5x_checkpoint_to_pytorch.py). This is particularly useful for converting [T5x Retrieval Dual Encoder](https://github.com/google-research/t5x_retrieval) Models to Pytorch.

To Use:

- In case you don't have gsutil, install according to https://cloud.google.com/storage/docs/gsutil_install
- Pretrained T5X_Retrieval checkpoints are at  https://console.cloud.google.com/storage/browser/t5-data/pretrained_models/t5x/retrieval/. Example:
gsutil -m cp -r : [gs://t5-data/pretrained_models/t5x/retrieval/gtr_base](https://console.cloud.google.com/storage/browser/t5-data/pretrained_models/t5x/retrieval/gtr_base/) $HOME/
- Create a corresponding config.json for the downloaded checkpoint. Often one already exists, e.g. here we can use https://huggingface.co/google/t5-v1_1-base/blob/main/config.json


I tested this on the GTR-base released checkpoint  and compared the Jax and Pytorch checkpoints  and the outputs are similar, 

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Models:

- text models: @ArthurZucker and @younesbelkada
- vision models: @amyeroberts and @NielsRogge
- speech models: @sanchit-gandhi

Library:

- flax: @sanchit-gandhi
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- tokenizers: @ArthurZucker
- trainer: @sgugger

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HF projects:

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- Flax: @sanchit-gandhi
- PyTorch: @sgugger
- TensorFlow: @Rocketknight1

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Comments:
_The documentation is not available anymore as the PR was closed or merged._

cc @ArthurZucker 

Once the tests are good we can merge!

Hi @ArthurZucker , `make style` seems to be changing a lot of files, is there any fix for this?

Yes, you probably have the wrong version of `black`. Something like `pip install --upgrade black` should fix this. 

Fixed🤓