* use vertex llm as base class for embeddings
* use correct vertex class in main.py
* set_headers in vertex llm base
* add types for vertex embedding requests
* add embedding handler for vertex
* use async mode for vertex embedding tests
* use vertexAI textEmbeddingConfig
* fix linting
* add sync and async mode testing for vertex ai embeddings
* add basic load test
* add vertex ai load test on ci cd
