feature: Allow config litellm.api_key and litellm.api_base by environment variables

[viralbhadeshiya]

Title

Allow config api_key & api_base by environment variable

Relevant issues

Feature #9075

Pre-Submission checklist

Please complete all items before asking a LiteLLM maintainer to review your PR

• [ ] I have Added testing in the tests/litellm/ directory, Adding at least 1 test is a hard requirement - see details
• [x] I have added a screenshot of my new test passing locally
• [x] My PR passes all unit tests on (make test-unit)[https://docs.litellm.ai/docs/extras/contributing_code]
• [x] My PR's scope is as isolated as possible, it only solves 1 specific problem

Type

🆕 New Feature

Changes

• Added support to read api_base & api_key form env variables. It will overwrite if these variable are specifically provided in code.
• Added Module notes so user can see it in function description.
• Unit test case result:

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Name	Status	Preview	Comments	Updated (UTC)
litellm	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Mar 13, 2025 6:21pm

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