Google GeminiPro support

[kamillitman]

Changes:

• [ ] New llm_models::GoogleModels enum with all the LLMModel trait methods implemented
• [ ] For GoogleModels::GeminProVertex (via Vertex AI) the code uses streaming and deserializes each response chunk, and for GoogleModels::GeminPro (via AI Studio) it just parses the full response
• [ ] New structs in domains module to deserialize GeminiPro API response
• [ ] New variables storing urls of Vertex and AI Studio APIs
• [ ] Testing code in examples/use_completions, including getting auth token for service ccount

[darioalessandro]

@kamillitman I think we need to bump the version