feat: support local auth

[k223kim]

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• Did you write any new necessary tests?

What does this PR do?

Non-studio users can use LitAI. The difference to this approach is the following:

• when lightning_api_key and lightning_user_id are given, no further auth
• only when there is no information of the user, this will redirect users to login through the browser (Demo: https://www.loom.com/share/567ce641f624418fb8b8811bb3409139?sid=3512aa8e-11d3-4819-9606-ace8cb6b4e0f)

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[aniketmaurya]

Looks good 🚀

Maybe we should be passing the lightning_api_key all the way where it is required rather than relying on env variable? (for a follow up of course)