Update propositional-retrieval template (#14766)

More descriptive name. Add parser in ingest. Update image link

templates/propositional-retrieval/propositional_retrieval/storage.py

@@ -0,0 +1,38 @@
+import logging
+from pathlib import Path
+
+from langchain.embeddings import OpenAIEmbeddings
+from langchain.retrievers.multi_vector import MultiVectorRetriever
+from langchain.storage import LocalFileStore
+from langchain_community.vectorstores import Chroma
+
+logging.basicConfig(level=logging.INFO)
+
+logger = logging.getLogger(__name__)
+
+
+def get_multi_vector_retriever(docstore_id_key: str):
+    """Create the composed retriever object."""
+    vectorstore = get_vectorstore()
+    store = get_docstore()
+    return MultiVectorRetriever(
+        vectorstore=vectorstore,
+        byte_store=store,
+        id_key=docstore_id_key,
+    )
+
+
+def get_vectorstore(collection_name: str = "proposals"):
+    """Get the vectorstore used for this example."""
+    return Chroma(
+        collection_name=collection_name,
+        persist_directory=str(Path(__file__).parent.parent / "chroma_db_proposals"),
+        embedding_function=OpenAIEmbeddings(),
+    )
+
+
+def get_docstore():
+    """Get the metadata store used for this example."""
+    return LocalFileStore(
+        str(Path(__file__).parent.parent / "multi_vector_retriever_metadata")
+    )