fix(timestamps): generate timestamps correctly and remove the deprecated pytz

[uptickmetachu]

Describe your changes

• Fixed timestamp generation so that it correctly reflects the time at the timezone. Previously timestamps were generated with the local machine time datetime.datetime.now() and then set to the timezone.
• I removed pytz as it is now deprecated since the inclusion of the built in zoneinfo

Issue number and link

Closes https://github.com/echoboomer/incident-bot/issues/453

Checklist before requesting a review

• [ ] I have properly bumped all version refs by running ./scripts/version-bump.sh v<new> from project root - for example ./scripts/version-bump.sh v1.9.3