Add OpenPI Dataset
Hi @Bharat123rox ! It looks like some of the dummy data is broken or missing. Did you auto-generate it? Does the local test pass for you? @yjernite requesting you to have a look as to why the tests are failing only on Windows, there seems to be a backslash error somewhere, could it be the result of `os.path.join` and what should be the fix for this? This is the `black` output locally:
```
(datasets_env) datasets (openpi) > black --check --line-length 119 --target-version py36 datasets/openpi/
All done! ✨ 🍰 ✨
1 file would be left unchanged.
``` Can you check your version of black (should be `20.8b1`) and run `make style again`? (And don't forget to rebase before pushing ;) )

The other test was a time-out error so should be good on the next commit Thanks @yjernite the CI tests finally passed!! Hi @Bharat123rox did you manage to join the different config into one using the IDs ?

Feel free to ping me when you're ready for the next review :)  > Hi @Bharat123rox did you manage to join the different config into one using the IDs ?
> 
> Feel free to ping me when you're ready for the next review :) 

Not yet @lhoestq still working on this! Meanwhile please review #1507 where I added the SelQA dataset :) Ok ! Let me review SelQA then :) 
Thanks for your help ! Apologies for the very late response. Here is the openpi dataset file with a single file per partition after merging `id_answers, answers.jsonl, question.jsonl , question_metadata.jsonl`

https://github.com/allenai/openpi-dataset/blob/main/data/gold-v1.1/dev.jsonl Nice thank you @nikett ! Hi @Bharat123rox , when you get a chance, please feel free to use the dataset from the repo ( [Link](https://github.com/allenai/openpi-dataset/blob/main/data/gold-v1.1/dev.jsonl) ) . Please let me know if any file is missing! Thank you 
Add the OpenPI Dataset by AI2 (AllenAI)