Add an article with inline blocks displaying products to the Demo module

Problem/Motivation

To showcase the features, we should add an example article to the demo.
This article should use Layout Builder and integrate two product lists into the article between texts: a block with all products from several categories (just choose random ones, to not stick to a specific store), and with products by SKU (again, random products or maybe from "most rated" or something). Generate the general article text using AI magic and store the node content (and layout config) in YAML.
Use a separate node bundle "commercetools Article" and clean up it on uninstall.
Add a test that checks that both blocks are present and contain products.