feat(dracut): add --sbat option to add sbat policy to UKI

feat(dracut): add --sbat option to add sbat policy to UKI

Take existing .sbat section from the uefi stub and merge it
with vmlinux .sbat (if it exists) and user-provided .sbat parameters
using the new --sbat option.

For some reasons, --update-section in objcopy does not resize the
.sbat section, so remove the section from the stub and add it
to the UKI as new one, to avoid having incomplete SBAT strings.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>