This is an experiment to attempt to make the provider independent of the operating system. The motivation is to be able to distribute it via the terraform registry (dmacvicar/terraform-provider-libvirt#747). As an experiment, it is not guaranteed that the changes will make into the main branch.
There are some command line (e.g. --min-memory and --adj-memory for autoballooning, also --networking-model in #20) switches that are better to have also in the configuration file that not introduced yet.
So the idea is to have a configuration file that will set all Default("...") in parameters for kingpin.