add utility class to perform N1QL/FTS queries with raw JSON response

Both FTS and N1QL request messages exist that allow to get the raw JSON response out of the service (either in String or ByteBuf form).

In order to make execution of these messages easier (especially those based on ByteBuf), an utility class outside of the Bucket API makes sense (as it would otherwise have to be a fully committed API, shared between SDKs).