Hide on-call schedules behind a feature flag

Add an `oncall_schedules_ff` feature flag

ee/app/finders/incident_management/oncall_schedules_finder.rb

@@ -19,7 +19,8 @@ module IncidentManagement
     attr_reader :current_user, :project, :params
 
     def available?
-      project.feature_available?(:oncall_schedules)
+      Feature.enabled?(:oncall_schedules_mvc, project) &&
+        project.feature_available?(:oncall_schedules)
     end
 
     def allowed?

ee/app/services/incident_management/oncall_schedules/create_service.rb

@@ -31,7 +31,8 @@ module IncidentManagement
       end
 
       def available?
-        project.feature_available?(:oncall_schedules)
+        Feature.enabled?(:oncall_schedules_mvc, project) &&
+          project.feature_available?(:oncall_schedules)
       end
 
       def error(message)

ee/config/feature_flags/development/oncall_schedules_mvc.yml

+---
+name: oncall_schedules_mvc
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/47407
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/283914
+milestone: '13.7'
+type: development
+group: group::monitor
+default_enabled: false

ee/spec/finders/incident_management/oncall_schedules_finder_spec.rb

@@ -24,6 +24,14 @@ RSpec.describe IncidentManagement::OncallSchedulesFinder do
         it 'returns project on-call schedules' do
           is_expected.to contain_exactly(oncall_schedule)
         end
+
+        context 'when feature flag is disabled' do
+          before do
+            stub_feature_flags(oncall_schedules_mvc: false)
+          end
+
+          it { is_expected.to eq(IncidentManagement::OncallSchedule.none) }
+        end
       end
 
       context 'when user has no permissions' do

ee/spec/services/incident_management/oncall_schedules/create_service_spec.rb

@@ -46,6 +46,14 @@ RSpec.describe IncidentManagement::OncallSchedules::CreateService do
       it_behaves_like 'error response', 'Your license does not support on-call schedules'
     end
 
+    context 'when feature flag is disabled' do
+      before do
+        stub_feature_flags(oncall_schedules_mvc: false)
+      end
+
+      it_behaves_like 'error response', 'Your license does not support on-call schedules'
+    end
+
     context 'when an on-call schedule already exists' do
       let!(:oncall_schedule) { create(:incident_management_oncall_schedule, project: project, name: 'On-call schedule') }