Added CLOVA studio Hyperclova X API support

[aschung01]

This PR adds support for the Hyperclova X API of CLOVA studio.

Product page Chat completeion API docs

Even though it's still in closed beta, Hyperclova X is extensively used by Korean startups and companies, thanks to its proficiency in Korean.

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Name	Status	Preview	Comments	Updated (UTC)
litellm	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Nov 27, 2023 2:38am

[krrishdholakia]

missing:

• exception mapping (check: exception_type())
• streaming support (check: CustomStreamWrapper)

@aschung01 the colab you shared on discord worked for me. If you can add these missing items, i think this is good for merge.

[aschung01]

I just added exception mapping & sync/async fake streaming, and added examples on the colab. Could you check it out? @krrishdholakia

[aschung01]

I've also modified model_prices_and_context_window.json because the JSON format wasn't consistent. Now the entire file follows a unified format.