feat: Add support for file-based secrets in config values

[bexelbie]

Title

Implement reading values (api_key, etc.) from files.

Relevant issues

Fixes #9240

Pre-Submission checklist

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• [X] 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 📖 Documentation ✅ Test

Changes

Added file/ as a valid config file marker for read from file similar to os.environ/ and oidc/ Tests added Docs added

Note: Linting and unit test failures unrelated to my code have been ignored.

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Name	Status	Preview	Comments	Updated (UTC)
litellm	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Mar 14, 2025 3:24pm

[bexelbie]

Let me know if this can be merged and I'll resolve the conflicts. Thank you

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All committers have signed the CLA.

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.