Configure ACLs for Copybara

This configures ACLs according to (internal) go/copybara-gerrit-acl.

Also adds a label, Presubmit-G3-Verified, which will be stamped by
Copybara on CLs passing G3 presubmits.

Bug: 448460564
Change-Id: Ic2a5f050fc1b3835475cc0eebd34cdfeb9fa5029
Reviewed-on: https://boringssl-review.googlesource.com/c/All-Projects/+/94187
Reviewed-by: David Benjamin <davidben@google.com>