feat: add API for fetching direct conversation with a user

- Added `GET /messages/conversations/with/:userId` endpoint in the backend to retrieve direct conversation data.
- Implemented corresponding method in `MessagesService` and `MessagesRepository`.
- Updated the frontend service to support fetching direct conversations via API.

frontend/src/services/message.service.ts

@@ -36,6 +36,13 @@ export const MessageService = {
 		return data;
 	},
 
+	async getConversationWith(userId: string): Promise<Conversation | null> {
+		const { data } = await api.get<Conversation | null>(
+			`/messages/conversations/with/${userId}`,
+		);
+		return data;
+	},
+
 	async sendMessage(recipientId: string, text: string): Promise<Message> {
 		const { data } = await api.post<Message>("/messages", {
 			recipientId,