Add Magma Agentic Model from Microsoft

[jwyang]

What does this PR do?

Add Microsoft Magma model to the repository

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[zucchini-nlp]

Yay, super excited to get the model shipped! I know it is early to review, I noticed the model doesn't have a modular file yet. I recommend to use modular transformers to add the model, it will allow you to inherit from any similar model in transformers and you won't have to rewrite the whole class

Also it makes the review process easier and faster, since we see what are the main differences between Magma and other exusting model 😉

[jwyang]

@zucchini-nlp , thank for the pointer! First time hearing about the modular transformers. I will take a look.