* feat - allow using gemini js SDK with LiteLLM
* add auth for gemini_proxy_route
* basic local test for js
* test cost tagging gemini js requests
* add js sdk test for gemini with litellm
* add docs on gemini JS SDK
* run node.js tests
* fix google ai studio tests
* fix vertex js spend test
* feat - allow tagging vertex JS SDK request
* add unit testing for passing headers for pass through endpoints
* fix allow using vertex_ai as the primary way for pass through vertex endpoints
* docs on vertex js pass tags
* add e2e test for vertex pass through with spend tags
* add e2e tests for streaming vertex JS with tags
* fix vertex ai testing