Update TAPAS script to convert TAPAS-NQ weights (re-attempt #11907)
Closes https://github.com/huggingface/transformers/issues/14494

This is a reattempt of #11907, as it became stall and was closed. I had to use the latest version and copy the code over.

Instructions:
* Clone fork
* go to `transformers/`
* `pip install torch pandas tensorflow`
* `pip install torch-scatter -f https://data.pyg.org/whl/torch-1.10.0+102.html` (or whatever your cu version is, just do `pip show torch` to find out)
* Download the retriever medium or large weights with HN from the official source: https://github.com/google-research/tapas/blob/master/DENSE_TABLE_RETRIEVER.md
* Run this:
```
# Medium model
python src/transformers/models/tapas/convert_tapas_original_tf_checkpoint_to_pytorch.py --task RETRIEVAL --tf_checkpoint_path tapas_nq_hn_retriever_medium/model.ckpt --tapas_config_file tapas_nq_hn_retriever_medium/bert_config.json --pytorch_dump_path tapas_od/ --vocab_file tapas_nq_hn_retriever_medium/vocab.txt 

# lareg model
python src/transformers/models/tapas/convert_tapas_original_tf_checkpoint_to_pytorch.py --task RETRIEVAL --tf_checkpoint_path tapas_nq_hn_retriever_large/model.ckpt --tapas_config_file tapas_nq_hn_retriever_large/bert_config.json --pytorch_dump_path tapas_nq_large/ --vocab_file tapas_nq_hn_retriever_large/vocab.txt 
```

## Results

https://huggingface.co/xhlu/tapas-nq-hn-retriever-medium-1
https://huggingface.co/xhlu/tapas-nq-hn-retriever-medium-0


https://huggingface.co/xhlu/tapas-nq-hn-retriever-large-1
https://huggingface.co/xhlu/tapas-nq-hn-retriever-large-0
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_15592). All of your documentation changes will be reflected on that endpoint.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.<|||||>@xhluca Thanks for this contribution! Can you elaborate how to use this for inference?<|||||>This script isn't meant for inference. You should use load the regular TAPAS model. I have uploaded them to Huggingface already so you can find my name and use them if you don't want to run this script.