Add admin_note permissions to epics

ee/app/policies/epic_policy.rb

@@ -3,6 +3,8 @@
 class EpicPolicy < BasePolicy
   delegate { @subject.group }
 
+  condition(:maintainer) { @subject.group.has_maintainer?(@user) }
+
   rule { can?(:read_epic) }.policy do
     enable :read_epic_iid
     enable :read_note
@@ -13,4 +15,6 @@ class EpicPolicy < BasePolicy
   end
 
   rule { can?(:create_note) }.enable :award_emoji
+
+  rule { maintainer }.enable :admin_note
 end