recovery_kernel: add signing type recovery_kernel

Taking as an input a recovery kernel, sign it with the recovery key (and
make sure to handle the old recovery keys tagged v1 too).

BUG=b:371248380
TEST=manual
BRANCH=None

Change-Id: I0631f9060bc5943c384f6b128a4d2389ba29dee0
Signed-off-by: Benjamin Shai <bshai@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/5996750
Reviewed-by: Julius Werner <jwerner@chromium.org>
Commit-Queue: ChromeOS Auto Runner <chromeos-auto-runner@chromeos-bot.iam.gserviceaccount.com>