Add GPTJForQuestionAnswering
# What does this PR do?

- Add `GPTJForQuestionAnswering` class for GPTJ upstream and QA downstream task

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Fixes # (issue)


## Before submitting
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [x] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [x] Did you write any new necessary tests?


## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

@patrickvonplaten, @LysandreJik
@sgugger, @patil-suraj

Hi, @sgugger and @patrickvonplaten again.
Like the https://github.com/huggingface/transformers/pull/13290 PR that I made before, I made QA for GPT-J class and made this PR for that.
If you have time, I'd appreciate your review and feedback on it.<|||||>This seems good to me - @patil-suraj, do you mind taking a look at this?<|||||>Looks good to me as well! @patil-suraj - could you also take a quick look? :-)<|||||>Thanks again for your PR!