Strip timezone from POST params

[kjduensing]

Summary

• This work is behind a feature toggle (flipper): YES

Related issue(s)

Closes department-of-veterans-affairs/va.gov-team#102843

Testing done

• New code is covered by unit tests

Acceptance criteria

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No error nor warning in the console.
• Events are being sent to the appropriate logging solution
• Documentation has been updated (link to documentation)
• No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs
• Feature/bug has a monitor built into Datadog (if applicable)
• If app impacted requires authentication, did you login to a local build and verify all authenticated routes work as expected

[liztownd]

Looks like you've got a linting error, but otherwise looks good!

[stevenjcumming]

Consider moving DateUtils and the other non-client models in /services to modules/travel_pay/lib/travel_pay in another PR