[Feature Request] Support modifying REST response codes and messages

Per #1846, enable support for a scenario like this. For example, use stored procedure response metadata to supplement HTTP response.

> Where and how do I specify custom status_code and exception messages in DAB? For example, I have a stored proc to read data and I want to return status_code 404 if the data not found. And in writing scenario, if my stored proc detect validation error, I want to return status_code 500 (Internal Error; or maybe even more customised user friendly message).