Fix tool calling for gemini

Title:

Updated request and response transformers for gemini models

Description: (optional)

Update response schema to handle multiple tools in response
Update request schema for tools


// Access your API key as an environment variable (see "Set up your API key" above)
const genAI = new GoogleGenerativeAI(process.env.API_KEY);

// ...

const generativeModel = genAI.getGenerativeModel({
  // Use a model that supports function calling, like a Gemini 1.5 model
  model: "gemini-1.5-flash",

  // Specify the function declaration.
  tools: {
    functionDeclarations: [controlLightFunctionDeclaration],
  },
});

Also added usage tokens while at it

Portkey-AI / gateway

Fix tool calling for gemini #426