verified-builds: add sha256 to image response

As part of verified builds, we need the sha256 of
generated artifacts (like images) in order to generate
provenance (signed metadata about the build).

BUG=chromium:1274931
TEST=none

Change-Id: Ic2babeb84ebedec34e711d042dbed237eaae8df4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/3469815
Reviewed-by: Greg Edelston <gredelston@google.com>
Reviewed-by: George Engelbrecht <engeg@google.com>
Commit-Queue: Yulan Lin <yulanlin@google.com>
3 files changed