rauc-mark-good.service: leverage systemd's sync target
rauc-mark-good.service: leverage systemd's sync target

systemd has a dedicated, special target called `boot-complete.target` that indicates,
that a boot-up is considered successful.

Citing the documentation[0]:
> This target is intended as generic synchronization point for services that shall determine or act on whether the boot process completed successfully. [...]

[0] https://www.freedesktop.org/software/systemd/man/systemd.special.html#boot-complete.target

Signed-off-by: Leif Middelschulte <cb1230b9781231980145bd09aa084be91325b23c@gmail.com>

rauc/meta-rauc,rauc/meta-rauc,rauc/meta-rauc,rauc/meta-rauc