V8 runs internal builders on public CLs. This creates a potential risk of exposing internal builder names by sending gatekeeper alerts to external authors unless 'forgiving_optional' is used consistent across all gatekeeper configs. This is somewhat non-obvious and based on logic deep in the gatekeeper implementation: https://cs.chromium.org/chromium/build/scripts/slave/gatekeeper_ng.py?l=685&rcl=fbb9984bd65e325235a5d9b5f41fe7e20556ae39.

To add another layer of protection from mistakes when changing gatekeeper configs or the referenced logic, we should add another explicit per-master setting to not send alerts to authors. Even better if we can teach gatekeeper to use luci-config and pull access information from there, although this is probably going to happen in luci-notify.

See comments on https://crrev.com/i/610587 for context.