Provide a way to set default keyboard config

[olberger]

AFAICS there's no standard way to set the keyboard defaults. It is likely that images may need to be customized in the parts of the world where qwerty isn't the most usual layout. So such a task would be quite helpful, in particular for environments like virtualbox where the user may be confronted to the image's console.

https://wiki.debian.org/Keyboard may help.