Add a mysql_session_timezone define to disable MySQL date functions

[cedx]

The problem: the Node.js driver for MySQL uses the DATE_ADD function to handle Date values. But MySQL date functions don't correctly handle daylight saving time.

Currently, on my servers using the Europe/Paris time zone, the queries generated give incorrect results:

SELECT UNIX_TIMESTAMP('2023-10-25 00:00:00');
-- 1698184800, same as: Date.fromString('2023-10-25 00:00:00').getTime() / 1000

SELECT DATE_ADD(FROM_UNIXTIME(0), INTERVAL 1698184800 SECOND);
-- 2023-10-24 23:00:00 !!!

This issue does not occur with the PHP/PDO driver which converts dates to yyyy-mm-dd hh:hh:ss strings.
https://github.com/haxetink/tink_sql/blob/master/src/tink/sql/drivers/php/PDO.hx#L86

This PR adds a mysql_session_timezone define to disable the use of MySQL date functions in the Node.js driver, bringing it into line with the PDO driver.