feat: Add RAG Indexing Service

[ishaansehgal99]

Reason for Change:
This PR introduces the RAG service. PR introduces the design for handling embeddings, vector stores, and CRUD operations for maintaining our RAG service index.

For the FAISS implementation we created a FaissVectorStoreManager to handle indexing, querying, updating, and deleting documents in a FAISS-based vector store.

The RAGOperations class handles CRUD operations, utilizing the vector store interface.

Additionally, we introduced abstract base classes for embedding models and vector stores. FastAPI endpoints have been used.