set content-type for streamed response (#968)

* set content-type for streamed response

* Changed to json lines

---------

Co-authored-by: Pamela Fox <[email protected]>

Author: kaygu

app/backend/app.py

@@ -165,6 +165,7 @@ async def chat():
         else:
             response = await make_response(format_as_ndjson(result))
             response.timeout = None  # type: ignore
+            response.mimetype = "application/json-lines"
             return response
     except Exception as error:
         return error_response(error, "/chat")