bot_scaling.proto: Add fields to support cost savings

Add fields to support calculation of per run cost savings, when compared
to max values for bots configured.

Bug: chromium:1077872
Change-Id: I925e0f400abe656ce97e9971e773196cd9fd2dce
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2180866
Reviewed-by: David Burger <dburger@chromium.org>
Reviewed-by: Dhanya Ganesh <dhanyaganesh@chromium.org>
Commit-Queue: Mike Nichols <mikenichols@chromium.org>
Tested-by: Mike Nichols <mikenichols@chromium.org>
2 files changed