Expose blip2qformer

[alex-jw-brooks]

This PR exposes Blip2QFormer so that it can be created via AutoModel.from_config, which is needed for making the projector component in granite speech generic (discussed in this PR).

Blip2QFormer is most of the way there already - this PR just:

• Handles AutoModel registration
• Adds docstrings / more information on forward inputs

Note that Blip2QFormer is already tested pretty extensively though the blip2 tests, and will also be tested through granite speech tests.

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@ArthurZucker can you please take a look?

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[zucchini-nlp]

Thanks for making it auto-mappable, looks good to me!

[alex-jw-brooks]

Awesome, thank you for the quick review @zucchini-nlp! I went ahead and rebased this pr to fix the conflict 🙂

[zucchini-nlp]

Thanks, we can merge when CI turns green