No back-date Check in appointment

[nus-se-script]

The bot allows you to add an appointment with a past dat. That shouldn't be possible

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_{[original: nus-cs2113-AY2324S2/pe-interim#1908] [original labels: type.FeatureFlaw severity.Medium]}

[L5-Z]

Team's Response

User has failed to read the UG carefully. It was clearly stated "Tracks both previous and upcoming medical appointments."

Duplicate status (if any):

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