Document relevant mixin usage patterns

[glpuga]

Description

The last few weeks have been rich in design proposals for problems we're likely to encounter again. Since we are

A few of these are probably worth keeping around as part of the permanent documentation, for

• Design documentation for third-parties.
• New developer onboarding.
• Archival. Lots of good godbolt examples that should not be lost and can potentially be reused.

Definition of done

• Define storage place. Linkable Doxygen docs, markdown documentation in repository, other?
• Define template. The pattern information as structured in the GoF book can be a start point: https://en.wikipedia.org/wiki/Software_design_pattern#Documentation
• Document general C++ mixin pattern as used in Ciabatta.
• Document Ivan's additive modules proposal described here.
• Document Nahuel's std::visit usage to create a filter factory proposed here and with a larger example in here.

Additional considerations

[olmerg]

I think that could be interesting to publish in a place like linkedin or medium

[hidmic]

Considering we are moving away from mixins, I'm inclined to close this ticket.

@glpuga please do if you agree.

[hidmic]

Closing this due to lack of activity.