Add check for an active alerts service

Check if alerts service is active for the project
before creating a GitLab issue from `NotifyService`

ee/app/services/projects/alerting/notify_service.rb

@@ -11,8 +11,8 @@ module Projects
       DEV_TOKEN = :development_token
 
       def execute(token)
+        return forbidden unless alerts_service_activated?
         return unauthorized unless valid_token?(token)
-        return forbidden unless create_issue?
 
         process_incident_issues
 
@@ -31,8 +31,10 @@ module Projects
         project.feature_available?(:incident_management)
       end
 
-      def create_issue?
-        incident_management_available? && generic_alert_endpoint_enabled?
+      def alerts_service_activated?
+        incident_management_available? &&
+          generic_alert_endpoint_enabled? &&
+          project.alerts_service.try(:active?)
       end
 
       def process_incident_issues

ee/spec/services/projects/alerting/notify_service_spec.rb

@@ -59,6 +59,9 @@ describe Projects::Alerting::NotifyService do
           stub_feature_flags(generic_alert_endpoint: true)
         end
 
+        context 'with activated Alerts Service' do
+          let!(:alerts_service) { create(:alerts_service, project: project) }
+
           context 'with valid token' do
             context 'with a valid payload' do
               it_behaves_like 'processes incident issues', 1
@@ -82,6 +85,13 @@ describe Projects::Alerting::NotifyService do
           end
         end
 
+        context 'with deactivated Alerts Service' do
+          let!(:alerts_service) { create(:alerts_service, :inactive, project: project) }
+
+          it_behaves_like 'does not process incident issues', http_status: 403
+        end
+      end
+
       context 'with Generic Alert Endpoint feature disabled' do
         before do
           stub_feature_flags(generic_alert_endpoint: false)