Add support for running autopkgtests

Ability to run autopkgtests inside the same container that is used for builds might make the overall test-fix-package-test -cycle turnaround time faster. Using hermetic throwaway containers for autopkgtests in general is a useful ability, but for packaging in particular it would super handy to be able to edit the autopkgtest code and quickly rerun it.

If Debcraft created automatic repositories of build packages, it could also offer the ability to run autopkgtest of other packages for the sake of testing that reverse dependencies don't break when running using the new package version from the thing being developed with the aid of Debcraft.

For testing autopkgtest good tricky packages are xdg-desktop-portal, bubblewrap, glib2; chrootkit and krb5.