Feature/promo banner

[ceciliatruong]

Describe your changes

• Created a promo-banner component with a ribbon highlighting "monthly promo", the cookie of the month, description of the cookie, and a learn more button that shows on all pages
• Wrote a function chooseCookieByMonth() to dynamically change the cookie of the month; user can alter the function to change the different cookies they want to highlight each month
• Created CSS for the promo banner and ribbon, there are still issues with the button not properly being adjusted with the different screen sizes

  Issue link

  https://github.com/codewithher/Web-C4C/issues/20 https://github.com/codewithher/Web-C4C/issues/14

  Checklist before requesting a review

• [x] I have confirmed that my updates are on the correct branch.
• [x] I have performed a self-review of my code.
• [x] I have performed a self-review of the updates on the browser.
• [x] I have confirmed that this update does not break anything else, visually or within the code.