project.config: grant submit access to the 1.21 release branch Also propagate the LUCI stuff. Change-Id: I2ef5700a056f968a028018079f02b1bdd3a9076a Reviewed-on: https://go-review.googlesource.com/c/All-Projects/+/510355 Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>