feat: add function and tools support for Gemini

[mxdlzg]

close #1348

我已确认该 PR 已自测通过，相关截图如下：
（此处放上测试通过的截图，如果不涉及前端改动或从 UI 上无法看出，请放终端启动成功的截图）

[SYS] 2024/04/23 - 15:36:34 | One API f0.6.5-f09 started 
[SYS] 2024/04/23 - 15:36:34 | running in debug mode 
[SYS] 2024/04/23 - 15:36:34 | using MySQL as database 
[SYS] 2024/04/23 - 15:36:34 | database migration started 
[SYS] 2024/04/23 - 15:36:34 | database migrated 
[SYS] 2024/04/23 - 15:36:34 | REDIS_CONN_STRING not set, Redis is not enabled 
[SYS] 2024/04/23 - 15:36:34 | using theme berry 
[SYS] 2024/04/23 - 15:36:34 | initializing token encoders 
[SYS] 2024/04/23 - 15:36:34 | token encoders initialized 
[DEBUG] 2024/04/23 - 15:36:51 | 2024042315365195072723771002422 | request body: {
    "model": "gemini-pro",
    "temperature": 0,
    "messages": [
        {
            "role": "user",
            "content": "用户所提出的问题是<Q>根据你自己的知识库回答教育的概念</Q>"
        }
    ],
    "tools": [
        {
            "type": "function",
            "function": {
                "name": "classify_question",
                "description": "结合对话记录及背景知识，对<Q></Q>内的用户问题进行分类，并返回对应的类型字段",
                "parameters": {
                    "type": "object",
                    "properties": {
                        "type": {
                            "type": "string",
                            "description": "问题类型。下面是几种可选的问题类型: 搜索知识库，返回：'wqre'；其它，返回：'sdfa'",
                            "enum": [
                                "wqre",
                                "sdfa"
                            ]
                        }
                    },
                    "required": [
                        "type"
                    ]
                }
            }
        }
    ],
    "tool_choice": {
        "type": "function",
        "function": {
            "name": "classify_question"
        }
    }
} 
[SYS] 2024/04/23 - 15:36:51 | failed to get token encoder for model gemini-pro: no encoding for model gemini-pro, using encoder for gpt-3.5-turbo 
[DEBUG] 2024/04/23 - 15:36:51 | 2024042315365195072723771002422 | converted request: 
{"contents":[{"role":"user","parts":[{"text":"用户所提出的问题是\u003cQ\u003e根据你自己的知识库回答教育的概念\u003c/Q\u003e"}]}],"safety_settings":[{"category":"HARM_CATEGORY_HARASSMENT","threshold":"BLOCK_NONE"},{"category":"HARM_CATEGORY_HATE_SPEECH","threshold":"BLOCK_NONE"},{"category":"HARM_CATEGORY_SEXUALLY_EXPLICIT","threshold":"BLOCK_NONE"},{"category":"HARM_CATEGORY_DANGEROUS_CONTENT","threshold":"BLOCK_NONE"}],"generation_config":{},"tools":[{"function_declarations":[{"description":"结合对话记录及背景知识，对\u003cQ\u003e\u003c/Q\u003e内的用户问题进行分类，并返回对应的类型字段","name":"classify_question","parameters":{"properties":{"type":{"description":"问题类型。下面是几种可选的问题类型: 搜索知识库，返回：'wqre'；其它，返回：'sdfa'","enum":["wqre","sdfa"],"type":"string"}},"required":["type"],"type":"object"}}]}]} 
[INFO] 2024/04/23 - 15:36:51 | 2024042315365195072723771002422 | user 1 has enough quota 499999979000798, trusted and no need to pre-consume 
[DEBUG] 2024/04/23 - 15:36:53 | 2024042315365195072723771002422 | response body: {
  "candidates": [
    {
      "content": {
        "parts": [
          {
            "functionCall": {
              "name": "classify_question",
              "args": {
                "type": "wqre"
              }
            }
          }
        ],
        "role": "model"
      },
      "finishReason": "STOP",
      "index": 0,
      "safetyRatings": [
        {
          "category": "HARM_CATEGORY_HARASSMENT",
          "probability": "NEGLIGIBLE"
        },
        {
          "category": "HARM_CATEGORY_HATE_SPEECH",
          "probability": "NEGLIGIBLE"
        },
        {
          "category": "HARM_CATEGORY_DANGEROUS_CONTENT",
          "probability": "NEGLIGIBLE"
        },
        {
          "category": "HARM_CATEGORY_SEXUALLY_EXPLICIT",
          "probability": "NEGLIGIBLE"
        }
      ]
    }
  ]
}

 
[GIN] 2024/04/23 - 15:36:53 | 2024042315365195072723771002422 | 200 |  2.036152357s |   xxx.xxx.146.1 |    POST /v1/chat/completions
[INFO] 2024/04/23 - 15:36:53 | 2024042315365195072723771002422 | record consume log: userId=1, channelId=4, promptTokens=43, completionTokens=0, modelName=gemini-pro, tokenName=FastChat, quota=43, content=模型倍率 1.00，分组倍率 1.00，补全倍率 3.00 

[songquanpeng]

Thx~