List LLM providers

{
  "providers": [
    {
      "base_url_hint": "string",
      "description": "string",
      "display_name": "string",
      "docs_url": "string",
      "key_placeholder": "string",
      "name": "string",
      "required_features": [
        "string"
      ],
      "requires_key": true
    }
  ]
}

{
  "detail": "Property foo is required but is missing.",
  "errors": [
    {
      "location": "string",
      "message": "string",
      "value": null
    }
  ],
  "instance": "https://example.com/error-log/abc123",
  "status": 400,
  "title": "Bad Request",
  "type": "https://example.com/errors/example"
}