Add ProgrammingGroup & ProgrammingGroupMembership

* User can create programming group with other users for exercise
* Submission is shared in a group
* Also adjust specs

spec/policies/programming_group_policy_spec.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe ProgrammingGroupPolicy do
+  subject(:policy) { described_class }
+
+  let(:programming_group) { build(:programming_group) }
+
+  %i[new? create?].each do |action|
+    permissions(action) do
+      it 'grants access to everyone' do
+        %i[external_user teacher admin].each do |factory_name|
+          expect(policy).to permit(create(factory_name), programming_group)
+        end
+      end
+    end
+  end
+end