justfile: Remove lorax recipe (replaced by image-builder)

See: https://fedoraproject.org/wiki/Changes/BuildAtomicDesktopsWithImageBuilder

justfile: Use zstd compression by default for container images

Default for Fedora 43+ and F42 will soon be EOL.

justfile: Generalize version logic

Push container images for Rawhide under their own version.

justfile: Also push rawhide images under the rawhide tag

justfile: Inline default variant name

justfile: Inline "default" arch value

justfile: Inline the --force-nocache option

generate-gitlab-ci: Update rawhide detection logic

Fixes: https://pagure.io/workstation-ostree-config/pull-request/751 (for container builds)