Add task TITLE not case insensitive

[nus-pe-bot]

UG states task with same title cannot be added

Expected : Task with same title as an existing task but in different case will not be added

Actual : Task added

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_{[original: nus-cs2103-AY2223S1/pe-interim#5509] [original labels: severity.Medium type.FunctionalityBug]}

[kianseong]

Team's Response

1. task add Add task storaGe
2. As shown in result display, task with same title in different case cannot be added with error message.

Duplicate status (if any):

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