Support for Vertex AI

[patryk20120]

Description

Add a basic model provider for Google Vertex AI LLM models and Text Embedding models.

Type of Change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)
• [x] This change requires a documentation update, included: Dify Document

How Has This Been Tested?

Testes by building an image and ran with front v0.6.8

• [ ] Tests

Suggested Checklist:

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings
• [x] I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods
• [ ] optional I have made corresponding changes to the documentation
• [ ] optional I have added tests that prove my fix is effective or that my feature works
• [ ] optional New and existing unit tests pass locally with my changes