Scripts with JSON datatype should be able to read data as String by default

ISPN-9182 introduced support for application/json as a script datatype, but the data is presented as byte[].

When protobuf is the storage, it is possible to read data as JSON from scripts in the String form, by applying the "type" parameters to the MediaType: "application/json; type=java.lang.String", but this is not available for other storages.