Summary:

This PR adds the getImageModel method to the Google Gemini TypeScript SDK, enabling the use of image generation models. This allows users to generate images using specified models, providing a smooth integration for image-based generative tasks.

Changes:

• Added getImageModel method in GoogleGenerativeAI class (src/gen-ai.ts) to initialize image generation models.
• Implemented ImageModel class (src/models/image-model.ts) to handle image generation requests.
• Updated generate-image.ts to include functionality for sending image generation requests.
• Introduced new types for image model parameters (src/types/requests.ts), such as BaseImageParams, ImageModelParams, and GenerateImageRequest.
• Updated the request logic to accommodate the image generation workflow.

Fixed Issues:

• Fixes Does this library supports image generation? #332: Adds image generation model support to the SDK.

Testing:

• Verify the integration of getImageModel for generating images with different configurations and model parameters.
• Test the image generation functionality through SDK methods to ensure valid API requests and responses.

Additional Notes:

• Added enums for safety filter levels and image prompt language (types/requests.ts).
• Enhanced error handling for missing model parameters in the getImageModel method.