Support for other llm's via Langchain

[dartpain]

Show how to switch in documentation

• [x] Test on different embeddings and different llm (e.g Huggingface embeds and Cohere llm)
• [x] Make sure different indexes can be used
• [ ] add all old vectorstores to new format in docshub
• [ ] Create documentation to show how to switch between LLM's
• [ ] Handle different embeddings in frontend
• [ ] Add embeddings path on DocsHUB (make it backwards compatable)