Sample App: Adding the graphics to the sample app tutorial

[Leo6Leo]

In order to make the the Sample App tutorial more engaging and visually appealing for the readers, and also to celebrate the recent publishing our Knative's new friend: Kuack, I am proposing hope incorporate Kuack into the design, and let him become the small "teacher duck", as I am sure he will add so much fun!

We can create a series of images featuring Kuack in various facial expressions and postures. These images will not only enrich our documentation but also have the potential to be transformed into stickers.

Here are some sample designs I have:

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[Leo6Leo]

/cc @knative/ux-wg-leads

[pierDipi]

Samples seem already cool! 😎