[AUR-392, AUR-413, AUR-414] Define base vector store, and make use of ChromaVectorStore from llama_index. Indexing and retrieving vectors with vector store (#18)

Design the base interface of vector store, and apply it to the Chroma Vector Store (wrapped around llama_index's implementation). Provide the pipelines to populate and retrieve from vector store.

knowledgehub/vectorstores/__init__.py

@@ -0,0 +1,4 @@
+from .base import BaseVectorStore
+from .chroma import ChromaVectorStore
+
+__all__ = ["BaseVectorStore", "ChromaVectorStore"]