Merge branch 'backport/group-policies' into 'master'

Backport hooks on group policies for the EE-specific implementation

See https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/822#note_19955431

See merge request !8066

app/policies/group_member_policy.rb

@@ -15,5 +15,11 @@ class GroupMemberPolicy < BasePolicy
     elsif @user == target_user
       can! :destroy_group_member
     end
+
+    additional_rules!
+  end
+
+  def additional_rules!
+    # This is meant to be overriden in EE
   end
 end

app/policies/group_policy.rb

@@ -33,6 +33,8 @@ class GroupPolicy < BasePolicy
     if globally_viewable && @subject.request_access_enabled && !member
       can! :request_access
     end
+
+    additional_rules!(master)
   end
 
   def can_read_group?
@@ -43,4 +45,8 @@ class GroupPolicy < BasePolicy
 
     GroupProjectsFinder.new(@subject).execute(@user).any?
   end
+
+  def additional_rules!(master)
+    # This is meant to be overriden in EE
+  end
 end