[frontend] Fix navigation and cart math

[julianocosta89]

Changes

Fix: #2659

A couple of big changes in this PR:

• Checkout page:
  • Now it shows address only once at the top
  • Product images are not distorted
  • The quantity of products are taken into consideration when buying the product
    • This is a funny one. Before this the price was always the same if there was 1 or 10 products of the same type in the cart.
• Cart dropdown:
  • Product images are not distorted anymore.
  • The scroll bar only appears when there is something to scroll.
• Footer:
  • Moved footer to the template and removed from all pages.
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  • This section recommends products not added to the cart users. When all items were added to the cart this section was empty.
    • Added a validation to remove the section when there are no items to show.

Merge Requirements

For new features contributions, please make sure you have completed the following
essential items:

• CHANGELOG.md updated to document new feature additions
• Appropriate documentation updates in the docs
• Appropriate Helm chart updates in the helm-charts

Maintainers will not merge until the above have been completed. If you're unsure
which docs need to be changed ping the
@open-telemetry/demo-approvers.