Change timestamp to ISO 8601

[ninxsoft]

sal-submit is currently logging timestamps as asctime, a human-readable format that does not provide any timezone information out-of-the-box:

2023-09-15 12:34:56,789

Proposing to change the default logging timestamp to an ISO 8601 compatible one with the timezone offset:

2023‐09‐15T12:34:56+1000

Caveats:

• The %z directive provides +HHMM / -HHMM style timezones offsets, omitting colons :, however this still qualifies as a valid ISO 8601 timestamp.
• There does not seem to be a valid directive to display milliseconds - is this important?