builder_config: Add a bool for unibuild

metadata.json needs this. I'm gonna add this in the config.

BUG=chromium:1064418
TEST=./generate.sh

Change-Id: I414958c517cbc28950196a17d1fe9bc1365ff92f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2130426
Tested-by: Dhanya Ganesh <dhanyaganesh@chromium.org>
Auto-Submit: Dhanya Ganesh <dhanyaganesh@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
Commit-Queue: David Burger <dburger@chromium.org>
2 files changed