I wanted automatic fsck for problems on the root filesystem,
and it was difficult to disconver that fsck.repair=yes
on the kernel cmdline is the way to configure that.

initramfs-tools was made to support the same configuration used by
systemd-fsck (#783410). So there is a documentation path in that
direction, but since I was trying to change the behavior of the
initramfs, which I know does not use systemd, I did not think to look in
systemd's documentation.