Support API's without Content-type

Re-evaluation; timeboxed to 1 SP.

Some api's not return content-type in the response, and actually response is empty. To support that we will do the following:

• Show a warning (log) the when api's not returning a content-type.
• Allow the user specify the content-type in the rest client definition.
• Add a filter that add the specified content-type to the response.