Produces a canonical nbpr artefact tarball from already-built files on disk.
mix nbpr.pack \
--package nbpr_jq \
--package-version 1.7.1 \
--system nerves_system_rpi4 \
--system-version 2.0.1 \
--target /path/to/built/target \
[--staging /path/to/built/staging] \
[--rootfs /path/to/built/rootfs] \
[--legal-info /path/to/built/legal-info] \
[--build-opts key=value,key2=value2] \
[-o /output/dir]Outputs a <package>-<version>-<system>-<system-version>-<key>.tar.gz in
-o (defaults to cwd). The tarball follows the layout consumed by
NBPR.Artifact.Cache.extract!/2.
Useful for hand-built artefacts (you ran Buildroot yourself) and as a
building block for the eventual mix nbpr.build task.