flatdeb-builder: Add script to enable binfmt

This MR applies the idea in !325 (merged) but taking into account the differences between release.

Since we need to support different approaches to enable binfmt create a script to use as wrapper.

In this way we avoid running checks in ci-flatpak-builder to enable it.

Signed-off-by: Walter Lozano walter.lozano@collabora.com