Add new kokoro reader group.

In order to support Kokoro's migration to Pod, GoB reader permissions will now be granted through the ACL group kokoro-gob-readers(-qa) instead of directly to borg roles kokoro/kokoro-dedicated(-qa).

See go/kokoro-gob-permissions-update and b/266422763 for more details.

groups

diff --git a/groups b/groups
index 1a5f50c..1731c35 100644
--- a/groups
+++ b/groups
@@ -11,3 +11,4 @@
 mdb:hafnium-admin                                             	mdb/hafnium-admin
 mdb:kokoro                                                    	mdb/kokoro
 mdb:kokoro-dedicated                                          	mdb/kokoro-dedicated
+mdb:kokoro-gob-readers                                        	mdb/kokoro-gob-readers

project.config

diff --git a/project.config b/project.config
index ce18ec9..f877806 100644
--- a/project.config
+++ b/project.config
@@ -16,6 +16,7 @@
 	read = group mdb/hafnium-admin
 	read = group mdb/kokoro
 	read = group mdb/kokoro-dedicated
+	read = group mdb/kokoro-gob-readers
 	removeReviewer = group mdb/gwsq
 	removeReviewer = group treehugger-robot
 	submit = group treehugger-robot