Support dynamic apiKeyHelper field for dynamic API key support

What feature would you like to see?

For leveraging custom implementations with OAuth, or where API keys refresh more frequently, support an apiKeyHelper command, like in Claude Code: https://docs.claude.com/en/docs/claude-code/llm-gateway

{
  "apiKeyHelper": "~/bin/get-litellm-key.sh"
}

Are you interested in implementing this feature?

Yes

Additional information

_No response_