community[patch]: Fixing embedchain document mapping (#18255)

- **Description:** The current embedchain implementation seems to handle
document metadata differently than done in the current implementation of
langchain and a KeyError is thrown. I would love for someone else to
test this...

---------

Co-authored-by: KKUGLER <kai.kugler@mercedes-benz.com>
Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>
Co-authored-by: Deshraj Yadav <deshraj@gatech.edu>

libs/community/langchain_community/retrievers/embedchain.py

@@ -65,7 +65,10 @@ class EmbedchainRetriever(BaseRetriever):
             docs.append(
                 Document(
                     page_content=r["context"],
-                    metadata={"source": r["source"], "document_id": r["document_id"]},
+                    metadata={
+                        "source": r["metadata"]["url"],
+                        "document_id": r["metadata"]["doc_id"],
+                    },
                 )
             )
         return docs