Fix document updateAt mapping (#254)

There was an issue with the updatedAt of a document showing another
document updatedAt. Specifically, the updatedAt in the document list
was being reversed and reflecting a different document's value.

This issue occured during the bulk retrieval of document lists using
yorkie-team/yorkie#931. In this process, there was no guarantee that the
order of the keys passed to the DB query matches the order of the
documents in the query result.

backend/src/workspace-documents/workspace-documents.service.ts

@@ -82,13 +82,16 @@ export class WorkspaceDocumentsService {
 		const yorkieDocumentList = await this.findManyFromYorkie(
 			slicedDocumentList.map((doc) => doc.yorkieDocumentId)
 		);
-		const mergedDocumentList = slicedDocumentList.map((doc, idx) => {
-			const yorkieDocument = yorkieDocumentList.documents?.[idx];
+		const yorkieDocumentMap = new Map(
+			yorkieDocumentList.documents?.map((doc) => [doc.key, doc])
+		);
+		const mergedDocumentList = slicedDocumentList.map((doc) => {
+			const yorkieDocumentUpdatedAt = yorkieDocumentMap.get(doc.yorkieDocumentId)?.updatedAt;
 
 			return {
 				...doc,
-				updatedAt: yorkieDocument?.updatedAt
-					? moment(yorkieDocument.updatedAt).toDate()
+				updatedAt: yorkieDocumentUpdatedAt
+					? moment(yorkieDocumentUpdatedAt).toDate()
 					: doc.updatedAt,
 			};
 		});