Add support for post-processing kwargs in image-text-to-text pipeline

[yonigozlan]

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

Who can review?

@Rocketknight1

[HuggingFaceDocBuilderDev]

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