scripts: add new scripts for configuring UKI

reset_uki_cmdline.sh empties the compiled-in command line. This is
necessary for the grub boot path to work, and the grub boot path is
configured by default. It will be used for unsigned images in vmtests.

set_uki_boot.sh configures the image to use a no-grub boot path. This
has to be run after signing occurs, because signing changes the kernel
command line and assumes that grub.cfg will work.

BUG=b/465210631
TEST=Local run on cchostdebug-amd64-gcp, result image booted
RELEASE_NOTE=None

Change-Id: Ia154ea68cde59e468677e80ac85e54847d51bebe
Reviewed-on: https://cos-review.googlesource.com/c/third_party/platform/crosutils/+/143605
Reviewed-by: He Gao <hegao@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>