Track epic issues count on usage data

Add epic issues count to
usage ping.

ee/changelogs/unreleased/issue_233156.yml

+---
+title: Track epic issue counts on usage ping
+merge_request: 50204
+author:
+type: other

ee/lib/ee/gitlab/usage_data.rb

@@ -192,6 +192,7 @@ module EE
                 confidential_epics: count(::Epic.confidential),
                 dependency_list_usages_total: redis_usage_data { ::Gitlab::UsageCounters::DependencyList.usage_totals[:total] },
                 epics: count(::Epic),
+                epic_issues: count(::EpicIssue),
                 feature_flags: count(Operations::FeatureFlag),
                 geo_nodes: count(::GeoNode),
                 geo_event_log_max_id: alt_usage_data { Geo::EventLog.maximum(:id) || 0 },

ee/spec/lib/ee/gitlab/usage_data_spec.rb

@@ -53,9 +53,12 @@ RSpec.describe Gitlab::UsageData do
       create(:status_page_setting, project: projects[0], enabled: true)
       create(:status_page_setting, project: projects[1], enabled: false)
       # 1 published issue on 1 projects with status page enabled
-      create(:issue, project: projects[0])
-      create(:issue, :published, project: projects[0])
+      issue_1 = create(:issue, project: projects[0])
+      issue_2 = create(:issue, :published, project: projects[0])
       create(:issue, :published, project: projects[1])
+
+      create(:epic_issue, issue: issue_2)
+      create(:epic_issue, issue: issue_1)
     end
 
     subject { described_class.data }
@@ -91,6 +94,7 @@ RSpec.describe Gitlab::UsageData do
         dependency_scanning_jobs
         epics
         epics_deepest_relationship_level
+        epic_issues
         feature_flags
         geo_nodes
         geo_event_log_max_id
@@ -126,6 +130,7 @@ RSpec.describe Gitlab::UsageData do
       expect(count_data[:status_page_issues]).to eq(1)
       expect(count_data[:issues_with_health_status]).to eq(2)
       expect(count_data[:projects_jira_issuelist_active]).to eq(1)
+      expect(count_data[:epic_issues]).to eq(2)
     end
 
     it 'has integer value for epic relationship level' do