Add file-based document store and vector store (#96)

* Modify docstore and vectorstore objects to be reconstructable
* Simplify the file docstore
* Use the simple file docstore and vector store in MVP

knowledgehub/storages/docstores/simple_file.py

@@ -0,0 +1,44 @@
+from pathlib import Path
+from typing import List, Optional, Union
+
+from kotaemon.base import Document
+
+from .in_memory import InMemoryDocumentStore
+
+
+class SimpleFileDocumentStore(InMemoryDocumentStore):
+    """Improve InMemoryDocumentStore by auto saving whenever the corpus is changed"""
+
+    def __init__(self, path: str | Path):
+        super().__init__()
+        self._path = path
+        if path is not None and Path(path).is_file():
+            self.load(path)
+
+    def add(
+        self,
+        docs: Union[Document, List[Document]],
+        ids: Optional[Union[List[str], str]] = None,
+        **kwargs,
+    ):
+        """Add document into document store
+
+        Args:
+            docs: list of documents to add
+            ids: specify the ids of documents to add or
+                use existing doc.doc_id
+            exist_ok: raise error when duplicate doc-id
+                found in the docstore (default to False)
+        """
+        super().add(docs=docs, ids=ids, **kwargs)
+        self.save(self._path)
+
+    def delete(self, ids: Union[List[str], str]):
+        """Delete document by id"""
+        super().delete(ids=ids)
+        self.save(self._path)
+
+    def __persist_flow__(self):
+        from theflow.utils.modules import serialize
+
+        return {"path": serialize(self._path)}