Refactor the index component and update the MVP insurance accordingly (#90)

Refactor the `kotaemon/pipelines` module to `kotaemon/indices`. Create the VectorIndex.

Note: currently I place `qa` to be inside `kotaemon/indices` since at the moment we only have `qa` in RAG. At the same time, I think `qa` can be an independent module in `kotaemon/qa`. Since this can be changed later, I still go at the 1st option for now to observe if we can change it later.

knowledgehub/indices/qa/__init__.py

@@ -0,0 +1,7 @@
+from .citation import CitationPipeline
+from .text_based import CitationQAPipeline
+
+__all__ = [
+    "CitationPipeline",
+    "CitationQAPipeline",
+]