Frontend: Fix ProductPreview Component #226

[Impressiv3]

Description

Fixed ProductPreview component so users cannot enter negative or way to high numbers while adding products to cart by using the input field or the +/- buttons.

Fixes # (issue) https://github.com/HackYourFuture-CPH/fp-class19/issues/226

How to test?

npm run storybook

Checklist

• [x] I have performed a self-review of my own code
• [x] I have followed the name conventions for CSS Classnames and filenames, Components names and filenames, Style filenames, if you are in doubt check the the project README.MD and here https://github.com/HackYourFuture-CPH/curriculum/blob/master/review/review-checklist.md
• [x] I have commented my code, particularly in hard-to-understand areas, if you code was simple enough mark the box anyway
• [x] I have made corresponding changes to the documentation, if you code was simple enough mark the box anyway
• [x] This PR is ready to be merged and not breaking any other functionality