Add timezone to MaxScale log timestamps

Being able to see which timezone the server is in makes issue analysis easier if there is a mix of timezones. For example, the MariaDB slow query log uses a UNIX timestamp which is always in UTC.

The current timestamp in the MaxScale logs is:

2026-05-12 08:59:52

The proposed timestamp for the EEST timezone would be:

2026-05-12 08:59:52+03:00

And for UTC it would be:

2026-05-12 08:59:52+00:00

An alternative would be to use an ISO 8601 timestamp which for EEST would be:

2026-05-12T08:59:52+03:00

And for UTC:

2026-05-12T08:59:52+00:00

OR

2026-05-12T08:59:52Z

Personally I find it a bit less readable than using a space as the separator for the date and time but it'd be a standard format.

A new setting for the log timestamp format would be useful for being able to revert to the old format. The proposed log_timestamp_format setting would have the following values:

• timestamp: The proposed new format YYYY-MM-DD HH:MM:SS+ZZ:ZZ where +ZZ:ZZ is the UTC offset.
• datetime: The old format of YYYY-MM-DD HH:MM:SS

ms_timestamp would still control whether fractional seconds are included but if we want to, we can add two extra options that would make it obsolete.