Add support for specifying output_content_type

[anandology]

Imagine you want to write a service to resize images. It should take an image as input and send back an image as output. The input part is handled by multipart/form-data, but there is no way to specify different output content type. Have an option in the config file to specify output_content_type and let the client return the response as bytes.

[palnabarun]

with this, is there a need for specifying the output content type?