tools: Add a script to switch between coreutils and rust-coreutils

These being essential packages, a script is needed to backup binaries used to do the upgrade.

https://phabricator.apertis.org/T8572

debian/changelog

+apertis-dev-tools (0.2021.8) apertis; urgency=medium
+
+  * Add a script to switch between coreutils and rust-coreutils
+
+ -- Detlev Casanova <detlev.casanova@collabora.com>  Mon, 21 Feb 2022 14:09:42 -0500
+
 apertis-dev-tools (0.2021.7) apertis; urgency=medium
 
   * pkg-merge-updatesi: Try to fast-forward before rebasing