Frontend: Update stock amount

[GreeshmaRahool]

Description

Update product's stock amount for every purchase

Fixes #280

How to test?

npm run dev

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

[GreeshmaRahool]

Great job @GreeshmaRahool 👍 Better Solution 🥇 Now the PR is working perfectly. Now, Its not only updating the stock amount after the purchase is complete, but also resetting the random value if the stock amount is zero. This is better solution than disabling the ADDTOCART button as you did it before.

Thanks @BikramRawat👍

[BikramRawat]

🥇