[Flax/run_hybrid_clip] Fix duplicating images when captions_per_image exceeds the number of captions, enable truncation
# What does this PR do?

Do not duplicate images when the number of captions in an example is smaller than `captions_per_image`.
Truncate tokens when number of tokens exceeds `max_length`.

Currently, if an example contains a number of captions smaller than `captions_per_image`, the dataset will get scrambled, because the image paths are going to be duplicated but the number of captions is not.
For example, if an example contains a single caption and `captions_per_image` is equal to 2, one caption will be appended to the captions list, but two image path will be appended to the `image_paths list`. This results in mismatching file_path-caption pairs.
This pull request fixes this issue.

Currently, if a tokenized sentence contains a number of tokens > `max_length`, the dimensions of inputs within a batch won't match.
This pull request fixes this issue by truncating the tokens to max_length.

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [X ] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
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      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/master/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/master/docs#writing-source-documentation).
- [ ] 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.

@patil-suraj 


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.

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