prototype: Add repeated BuilderConfig message to milestone message.

In the prototype protos for release configuration add a repeated
BuilderConfig message to the milestone message. This allows for the
definition of what will run at a milestone. Next step would be to cook
up such a config in other prototyping locations.

BUG=None
TEST=./generate.sh

Change-Id: I5d93677edfcd73321a1c2922461a2becdad674f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2399678
Reviewed-by: Mike Nichols <mikenichols@chromium.org>
Reviewed-by: Andrew Lamb <andrewlamb@chromium.org>
Reviewed-by: C Shapiro <shapiroc@chromium.org>
Commit-Queue: David Burger <dburger@chromium.org>
Tested-by: David Burger <dburger@chromium.org>
4 files changed