feat(config): Enable All Config Parameters via Environment Variables

[pankaj-bind]

Description

Added support to configure all gateway settings using environment variables instead of just config.yml. Now you can set any config parameter via env vars with GATEWAY_ prefix. Complex fields like providers and pricing can be set using JSON strings.

PR Type

🆕 New Feature

Relevant issues

Fixes #610

Changes Made

• Modified config.py to support env vars for all fields with proper precedence
• Added JSON parsing for complex nested configs (providers, pricing, etc.)
• Environment variables now take precedence over file config
• Added comprehensive unit tests in test_gateway_config.py

Checklist

• I have added unit tests that prove my fix/feature works
• New and existing tests pass locally
• Documentation was updated where necessary
• I have read and followed the contribution guidelines

[github-actions]

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