Optionally keep EIB assets and/or artifacts

[e-minguez]

Currently the combustion and artifacts folder is wiped https://github.com/suse-edge/edge-image-builder/blob/main/pkg/combustion/templates/cleanup-combustion.sh
It would be nice to make this optional or at least keep some files (the eib definition file? all the text files?) on the final host.

The reason behind this is because even if the source of truth eib definition file should be stored somewhere safely and outside the cluster, perhaps it can be lost or damaged for whatever reason and it would be really helpful to keep it (and other assets) optionally on the running host for troubleshooting purposes.

[e-minguez]

Just in case, in other operating systems, by default, a /root/anaconda-ks.cfg is created with all the installation options you selected on a manual installation

[jdob]

Quick note: we can't keep the definition on the running node until we fix the plain text secrets problem (sccRegistrationCode). We know we need to do that, we just haven't gotten to it yet.