Spring-ai Add "role": "function" to Gemini API Function Calling Results

Expected Behavior I want to set role to "function" in the content of the Gemini API function call result. That is because in the "Multi-turn function calling curl example request" example in the Gemini API documentation, role is set to "function".

https://ai.google.dev/gemini-api/docs/function-calling#expandable-7

"role":"function" attribute is consistent with best practices observed in other major APIs such as OpenAI's GPT. This clear role assignment improves readability and debugging and makes it easier for developers to understand and manage the flow of function calls and responses.

Currently, the lack of a "role" attribute in the result of a function call makes it difficult to distinguish between different parts of the interaction, potentially leading to confusion and response processing errors. Explicitly setting "role" to "function" will make the structure of the response clearer and more consistent with the examples in the Gemini API documentation.

{
  "contents": [
    {
      "role": "user",
      "parts": [
        {
          "text": ...
        }
      ]
    },
    {
      "role": "model",
      "parts": [
        {
          "functionCall": {
            ...
          }
        }
      ]
    },
    {
      "role": "function",
      "parts": [
        {
          "functionResponse": {
            ...
          }
        }
      ]
    }
  ]
}

Current Behavior The content of the Function Calling result of the Gemini API does not include a "role".

{
  "contents": [
    {
      "role": "user",
      "parts": [
        {
          "text": ...
        }
      ]
    },
    {
      "role": "model",
      "parts": [
        {
          "functionCall": {
            ...
          }
        }
      ]
    },
    {
      "parts": [
        {
          "functionResponse": {
            ...
          }
        }
      ]
    }
  ]
}

Comment From: e1arikawa

PR created. thanks. https://github.com/spring-projects/spring-ai/pull/870