Draft: Add Testimonials Tab

Changes Made:

• This is an attempt at the UI for the new Course Testimonials feature (where users can add their experiences/recommendations on courses they've taken), feel free to comment on anything to improve the code/suggest any changes!

Here is a short description on what the functions do/refer to:

• ReviewCard - each card that appears upon expanding each course detail panel.
• ReviewsTable - the react-mantine-table containing all of the courses.
• TestimonialsPage - the whole page.