Deliver kickstart tree files stored within the registry as OCI artifact

In order to provision a bare-metal cluster from a bootable container one needs corresponding kickstart files (bootloader, kernel, initramdisk). The goal is to store and have shipped PXE netboot files in the container registry as as OCI artifacts alongside the bootc container image. This way during the provisioning phase a container registry will be the only infrastructure needed and interacted with.

Proposed specs to standardize the format of PXE netboot files as OCI artifact can be found here https://github.com/pulp/kickstart-oci-specs

• created repo for the fedora pipeline https://gitlab.com/fedora/bootc/artifacts/kickstart-artifacts
• ticket to get created according fedora repo on quay.io https://pagure.io/fedora-infrastructure/issue/12152
• official FC42 change based on the community feedback https://fedoraproject.org/wiki/Changes/KickstartOciArtifacts