Add new OnboardingExperimentHelper modules

OnboardingExperimentHelpers take care of
determining if the current_user should or should
not see the new onboarding feature.

app/helpers/onboarding_experiment_helper.rb

+# frozen_string_literal: true
+
+module OnboardingExperimentHelper
+  def allow_access_to_onboarding?
+    ::Gitlab.com? && Feature.enabled?(:user_onboarding)
+  end
+end

spec/helpers/onboarding_experiment_helper_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe OnboardingExperimentHelper, type: :helper do
+  describe '.allow_access_to_onboarding?' do
+    context "when we're not gitlab.com" do
+      it 'returns false' do
+        allow(::Gitlab).to receive(:com?).and_return(false)
+
+        expect(helper.allow_access_to_onboarding?).to be(false)
+      end
+    end
+
+    context "when we're gitlab.com" do
+      before do
+        allow(::Gitlab).to receive(:com?).and_return(true)
+      end
+
+      context 'and the :user_onboarding feature is not enabled' do
+        it 'returns false' do
+          stub_feature_flags(user_onboarding: false)
+
+          expect(helper.allow_access_to_onboarding?).to be(false)
+        end
+      end
+
+      context 'and the :user_onboarding feature is enabled' do
+        it 'returns true' do
+          stub_feature_flags(user_onboarding: true)
+          allow(helper).to receive(:current_user).and_return(create(:user))
+
+          expect(helper.allow_access_to_onboarding?).to be(true)
+        end
+      end
+    end
+  end
+end