Able to add duplicate habits

[nus-pe-bot]

'clean' habit can be added twice to habit list.

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_{[original: nus-cs2113-AY2324S2/pe-interim#2551] [original labels: type.FunctionalityBug severity.Medium]}

[genexus85]

Team's Response

Bug severity should be low instead, as having a duplicate habit is unlikely to affect normal operations of the habit tracker. In the case of having a duplicate habit, the user can use the "habit delete" command to delete the duplicate bug.

Duplicate status (if any):

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