feat: hints on failed checks

[dyga01]

Description: Gatorgrade does not have a feature that allows instructors to add hints that will be displayed anytime a check fails. This can make it difficult for students to understand why checks are failing, specifically for 100-level classes.

Solution: This feature would display a hint, usually some additional useful information, anytime a check fails. Instructors can set hints for specific checks within the gatorgrade.yml file.