adding auth, showing user or guest

[varsha84]

Description

This PR is to use auth in cart page using firebase. Since base on shopping cart context functionality implemented by Yones, it is clear now that shopping cart will use the local storage for storing the cart items. hence a user without login can also add the item in his shopping cart with creating any database entry (in order table).
I will update the shopping cart functionality in another PR ( getting shopping cart item from localStorage)

Fixes #226

How to test?

npm run dev go to cart page localhost/cart/4

1. as authenticated user ( it must show your name and email)
2. if not authenticated, it only show name as "Guest"

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
• [ ] This PR is ready to be merged and not breaking any other functionality

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