[BACKEND] [DEFECT] Properly implement timestamps using IANA Timezones and UTC offsets

[jji05]

Is your feature request related to a problem? Please describe.

We have a really jank timezone parsing method by using UTC for everything. We should be properly handling timezones since Payload properly supports them starting from version 3.71.0.

https://github.com/payloadcms/payload/releases/tag/v3.71.0

Describe the solution you'd like

We will probably need to PR this and implement this fix in a future semester to avoid past migrations from UTC time(massive tech debt).

BEFORE MERGING

• Integration test written for services
• Schemas annotated if adding new models
• Code generation run (hint: pnpm generate:types)
• Appropriate mocks created where possible
• PR Reviewed (For non-trivial changes)
• Changes tested after rebasing on master or merging in master (hint: git fetch origin master:master, then git rebase master or git merge master)
• All required PR checks passing