SQL: have the drivers (JDBC/ODBC) respond with ISO8601 formatted dates

The SQL protocol, as it stands now, makes a difference between the drivers' responses and REST/CLI responses when it comes to date fields: for JDBC/ODBC these are returned as millis since epoch, while for the rest of request types they are returned as ISO8601 formatted Strings.
We should return ISO8601 formatted String for the drivers, as well.