[PE-D] Invalid tutorial group is allowed

[nus-se-script]

Steps to reproduce:

add n/John Doe tg/CS2100 G e/e0123456@u.nus.edu

add n/John Doe tg/CS2100 9 e/e0123456@u.nus.edu

Issue: For input in tg/, there is a check for valid module code but no check for valid tutorial group. A tutorial group consist of at least one character and at least one number.

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Labels: type.FunctionalityBug severity.Low original: jinnhl/ped#6

[LowJiaHao99]

Tutorial group can be added based on TA's preference. A TA may want to omit the starting characters of a tutorial group since the tutorial groups in a module uses the same letter