Experimental Gemini 2.0 Flash image generation, gemma-3-27b-it and YouTube URL input

Model updates:

• Launched an experimental Gemini 2.0 Flash model capable of image generation and editing.
• Released gemma-3-27b-it, available on AI Studio and through the Gemini API, as part of the Gemma 3 launch.

API updates:

• Added support for YouTube URLs as a media source.
• Added support for including an inline video of less than 20MB.