204 responses handling in ruby

[baywet]

related #1410

Two main cases are possible:

The endpoint is described to only return 204, in which case we should have a request adapter method that returns void (might not be required due to the dynamic nature of the language making it possible to reuse existing methods). In which case the executor method generation needs to be updated like other languages.

The endpoint is described to return a success status code, but we get a 204 response at runtime. In which case the request adapter implementation should be updated so it doesn't try to access the response body to deserialize it, and simply to return null instead.

[baywet]

superseded by #1827