feat: update date-fns to v4, migrate to @date-fns/tz

[karrui]

TL;DR

Updated date-fns dependencies and migrated timezone handling to use the new @date-fns/tz package.

What changed?

• Upgraded date-fns from v3.6.0 to v4.1.0
• Replaced date-fns-tz with @date-fns/tz v1.2.0
• Updated email router to use TZDate from @date-fns/tz for timezone handling
• Modified date formatting in the email template to use the new format function

How to test?

1. Request an email OTP
2. Verify the received email shows the correct expiration time in Singapore timezone
3. Confirm the OTP functionality works as expected
4. Verify the date format matches "dd MMM yyyy, h:mmaaa" pattern

Why make this change?

The update to date-fns v4 and migration to @date-fns/tz provides better timezone handling and maintains compatibility with the latest date manipulation libraries. This change ensures consistent date formatting across the application while using modern, supported packages.

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
starter-kit	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Nov 13, 2024 8:21am

[karrui]

• feat: update date-fns to v4, migrate to @date-fns/tz #354 👈
• main

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[datadog-opengovsg]

Datadog Report

Branch report: 11-13-feat_update_date-fns_use_date-fns_tz
Commit report: 518716f
Test service: starter-kit

✅ 0 Failed, 11 Passed, 0 Skipped, 16.11s Total Time
➡️ Test Sessions change in coverage: 1 no change