Add usage ping metric to count alert services

ee/changelogs/unreleased/usage-ping-for-alerts.yml

+---
+title: Add a usage ping metric for number of activated Alert Services
+merge_request: 19765
+author:
+type: added

ee/lib/ee/gitlab/usage_data.rb

@@ -137,7 +137,8 @@ module EE
                                          projects_reporting_ci_cd_back_to_github: count(::GithubService.without_defaults.active),
                                          projects_with_packages: count(::Packages::Package.select('distinct project_id')),
                                          projects_with_prometheus_alerts: count(PrometheusAlert.distinct_projects),
-                                         projects_with_tracing_enabled: count(ProjectTracingSetting)
+                                         projects_with_tracing_enabled: count(ProjectTracingSetting),
+                                         projects_with_alerts_service_enabled: count(AlertsService.active)
                                        },
                                        service_desk_counts,
                                        security_products_usage,

ee/spec/lib/gitlab/usage_data_spec.rb

@@ -24,6 +24,9 @@ describe Gitlab::UsageData do
       create(:prometheus_alert, project: projects[0])
       create(:prometheus_alert, project: projects[1])
 
+      create(:alerts_service, project: projects[0])
+      create(:alerts_service, :inactive, project: projects[1])
+
       create(:package, project: projects[0])
       create(:package, project: projects[0])
       create(:package, project: projects[1])
@@ -83,6 +86,7 @@ describe Gitlab::UsageData do
         projects_with_packages
         projects_with_prometheus_alerts
         projects_with_tracing_enabled
+        projects_with_alerts_service_enabled
         sast_jobs
         design_management_designs_create
         design_management_designs_update
@@ -94,6 +98,7 @@ describe Gitlab::UsageData do
       expect(count_data[:projects_with_prometheus_alerts]).to eq(2)
       expect(count_data[:projects_with_packages]).to eq(2)
       expect(count_data[:feature_flags]).to eq(1)
+      expect(count_data[:projects_with_alerts_service_enabled]).to eq(1)
     end
 
     it 'has integer value for epic relationship level' do