add: Allow auth extra_headers to be set via .env

[gkaretka]

Title

Allow auth extra_headers to be set via .env

Relevant issues

none

Pre-Submission checklist

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

• [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

Changes

• Allow extra_headers to be set via .env
• Add env to docs

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Name	Status	Preview	Comments	Updated (UTC)
litellm	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Apr 24, 2025 2:21pm

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[gkaretka]

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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.