Parameters passed to systemd-repart are now passed to the build script
via environment variable, which is defined as a list of strings in
combination with `__structuredAttrs = true`. This should make it easier
to customize the image build using `overrideAttrs`.
Both the script used to amend the repart definitions and the amended
definitions are now available via passthru.
The version option is needed if you want to implement partition &
systemd-boot based A/B booting where the version information is encoded
in the files on the ESP. See systemd-sysupate docs for more details on
this:
https://www.freedesktop.org/software/systemd/man/latest/sysupdate.d.html
Note, however, that this is not *only* useful for systemd-sysupdate but
also for other similar updating tools/mechanisms.
Since the repart image is built on the build platform, use
`buildPackages` to construct the image. This allows for systemd-repart
images for cross-compiled nixos configurations to work properly.
