BLIPs clean-up

[zucchini-nlp]

What does this PR do?

Continuation of #34502, do not review yet

Main changes:

• Clean up the if/else cases and leave only the new logic with expanded inputs
• Change the Blip2Retrieval model class to accept expanded inputs (open to feedback). Currently it expects non-expanded inputs to do ITM so I just cropped the inputs, will think of a better solution
• Open PRs on the hub for the two checkpoints for Blip2Retrieval

[HuggingFaceDocBuilderDev]

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