Javascript in add-ons. Explain the Plone 6 way.

[ksuess]

The upgrade guide mentions already this topic: https://6.docs.plone.org/backend/upgrading/version-specific-migration/upgrade-to-60.html#mockup-and-resource-registry-redone
A more detailed "How To" would be helpful. With code and screenshots and examples of add-ons that do it the recommended way.

Placeholder is already there: https://6.docs.plone.org/classic-ui/static-resources.html

Suggested outline

• What's the purpose of patterns?
• Show me an example implementation. In which files is it applied? What does the code look like?
• How do I write a pattern? plonecli, bobtemplates, other?
• How do I register resources, such as JavaScript, images, and CSS?
• Do I have to minify or does Plone minify?
• Where does jQuery fit into patterns?
• Does module federation affect me?
• Where would should this chapter be located? In classic-ui or classic-ui/theming?

[ksuess]

This PR could be a starting point: #1275