Make downstream customizations easier

• 7a7a6086 Drop .arcconfig
• 762569b0 Drop the apertis- prefix from the image folders
• e31564d0 base: Rename the recipe to rootfs.yaml
• c1e1ca77 base: Rename the ospack file to a neutral "rootfs"
• 7d4bce20 Drop the APT GPG key from images that get it via the base container
• 71ee8782 Make the OS name configurable
• c053666f Make the APT mirror easier to customize

base/Dockerfile

@@ -25,7 +25,7 @@ ENV LC_ALL=C.UTF-8
 
 ARG DEBIAN_FRONTEND=noninteractive
 
-ARG OSPACK=apertis.tar.gz
+ARG OSPACK=rootfs.tar.gz
 ADD ${OSPACK} /
 
 # Always install procps in case the docker file gets used in jenkins