feat: Book image on home page now directs to book's Amazon page

[Joshua-Lester3]

Description

The book image showing the Essential C# 12.0 cover is now clickable. Clicking it opens Amazon's page for the book.

No open issue for this.

Ensure that your pull request has followed all the steps below:

• Code compilation
• Created tests which fail without the change (if possible) - N/A
• All tests passing - EssentialCSharp.Web.Tests.FunctionalTests.WhenTheApplicationStarts_ItCanLoadLoadPages(relativeUrl: "/guidelines") does not pass. I believe it's supposed to be pulling from EssentialCSharp.Web/Guidelines/guidelines.json but that does not exist. I'm not sure where it comes from, but I'm going to assume it's handled elsewhere.
• Extended the README / documentation, if necessary - N/A

[BenjaminMichaelis]

This LGTM

Let's