c0aeff4b99 added this in one unit file, but the
same problem occurs here. (There are no other files where this would apply.)
I think we should solve this systematically somehow, but it's not clear how to
do that, so until we have that better solution, let's apply the manual solution
so that our units work as expected.
Most of our kernel cmdline options use underscores as word separators in
kernel cmdline options, but there were some exceptions. Let's fix those,
and also use underscores.
Since our /proc/cmdline parsers don't distinguish between the two
characters anyway this should not break anything, but makes sure our own
codebase (and in particular docs and log messages) are internally
consistent.
Let's rename the unit to systemd-battery-check.service. We usually want
to name our own unit files like our tools they wrap, in particular if
they are entirely defined by us (i.e. not just wrappers of foreign
concepts)
While we are at it, also hook this in from initrd.target, and order it
against initrd-root-device.target so that it runs before the root device
is possibly written to (i.e. mounted or fsck'ed).
This is heavily inspired by @aafeijoo-suse's PR #28208, but quite
different ;-)
