Gemini 1.5 Pro Preview, Text Embeddings 004, File API, and More

Model updates:

• Released Gemini 1.5 Pro (gemini-1.5-pro-latest) in preview.
• Released text-embeddings-004 with support for elastic embedding sizes under 768.

API updates:

• Released the File API for temporarily storing media files.
• Added support for multimodal prompting (text, image, and audio).
• Released System instructions in beta.
• Added Function calling mode.
• Added response_mime_type configuration option for JSON format responses.