Add Vertex AI Gemini support

[ghchinoy]

Would like to see full GCP usage including Vertex AI Gemini usage rather than OpenAI.

Bonus would be to use any Vertex AI Model Garden model (like Llama or Claude)

[sotazum]

Hi, thank you for bringing up the issue.

You can choose the model you prefer on the Dify UI, including Gemini. Our Terraform code does not include any modules related to LLM models. The architecture image in the README is simply one example.