Limit "Submit" permission

Revoke "Submit" permission from all but the CQ service account and
Administrators.

Change-Id: I53da0fdaf2f2a43c2111c1b83c66bdfb1dc76b4b
Reviewed-on: https://pigweed-review.googlesource.com/c/Public-Commit-Queue-Projects/+/92325
Reviewed-by: Marc-Antoine Ruel <maruel@google.com>

project.config

diff --git a/project.config b/project.config
index d2c7631..762699f 100644
--- a/project.config
+++ b/project.config
@@ -19,11 +19,13 @@
 	labelAs-Commit-Queue = +0..+2 group Commit Queue
 	push = group Commit Queue
 	read = group Commit Queue
+	submit = group Administrators
 	submit = group Commit Queue
 	label-Code-Review = +0..+2 group Pigweed Integration Roller
 	label-Code-Review = +0..+2 group Pigweed Roller
 	label-Pigweed-Auto-Submit = +0..+1 group Pigweed Source Committers
 	rebase = group Auto Submit
+	exclusiveGroupPermissions = submit
 [project]
 	description = Public projects using CQ.
 [label "Pigweed-Auto-Submit"]