Optimize transfer-encoding for http-kafka correlated response

[jfallows]

Currently, when we deliver the correlated response for http-kafka produce capability bindings, we omit the content-length so in HTTP/1.1 the response uses chunked transfer-encoding due to indeterminate length.

Instead we should use the kafka deferred length to set the http response content-length in http-kafka, then HTTP/1.1 will no longer need to use chunked transfer-encoding.