#5903284 Components: Add new top-level component to display list of links with icons and descriptions

This pull request extracts the components responsible for displaying a list of navigation links with icons and descriptions from the domain management section:

This refactoring introduces a new VerticalNavItemEnhanced component that will allow us to show such a list in any part of Calypso. Those changes were extracted from #52755.

Testing instructions

1. Run git checkout add/vertical-nav-item-enhanced and start your server, or open a live branch
2. Log into a WordPress.com with a domain
3. Open the Domains page
4. Click on that domain
5. Assert that the Domain Settings page displays like before
6. Open the documentation page of the VerticalNav component
7. Assert that the example now shows two new items with icons and descriptions