Add support for post-processing kwargs in image-text-to-text pipeline
Author: yonigozlan
Pull request: yes

# What does this PR do?

This PR adds support for post-processing kwargs for the image-text-to-text pipeline. Following what is done in the text-generation pipeline, for now only `clean_up_tokenization_spaces` is supported, but more can be added in the future.

It also fixes two bugs with the pipeline
- One where the preprocessing kwargs given in the init of the pipeline would be overriden when calling it with no preprocessing kwargs.
- Another where the pipeline would crash with chat templates when `images=image` where image is not a list

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## Who can review?

@Rocketknight1 

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Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_35374). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

Gentle ping @Rocketknight1 , if you have some bandwidth to review this PR :)