[PE-D][Tester A] Appointment date can be later than today's date

[nus-se-bot]

steps to reproduce:

1. enter command schedule patient=Alex Yeoh start=2000/10/20 12:00 end=2000/10/20 13:00 description=Follow up on Chest X-Ray priority=high

Expected: MediFlowR to flag out appointment date is outdated

Actual: Appointment successfully set

If being able to add an outdated date is intended, i feel that it will be better to inform the user about it, in case the outdated date was a typo and the appointment date will be incorrectly set

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Labels: type.FunctionalityBug severity.VeryLow
original: CelestineTan03/ped#10

[trgao]

We want to keep track of all appointments even if it had passed