replace debos by mmdebstrap in SimpleSystemImageBuild

User story

debos fails with recent user-mode-linux (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1086194), lacks architecture support and is slow in CI. @helmutg came up with some scripts to replace it by mmdebstrap.

Error handling

As mmdebstrap works without starting a VM it should improve a lot.

Implementation plan

Helmut wrote a first version of the needed scripts. We need to refine them to make sure they fit the task. On the debusine side we need to replace the debos calls and make sure all needed features are migrated.

Open questions

• Where to put the scripts? Helmut offered to ship them in debvm but we may also ship them in debusine till they are finalized and available in bookworm.

Notes