Add usage metric around agents which have a token

changelogs/unreleased/usage_ping_agent_token.yml

+---
+title: Add usage ping for distinct count for kubernetes agents for at least one token
+merge_request: 40563
+author:
+type: other

lib/gitlab/usage_data.rb

@@ -112,6 +112,7 @@ module Gitlab
             clusters_applications_cilium: count(::Clusters::Applications::Cilium.available),
             clusters_management_project: count(::Clusters::Cluster.with_management_project),
             kubernetes_agents: count(::Clusters::Agent),
+            kubernetes_agents_with_token: distinct_count(::Clusters::AgentToken, :agent_id),
             in_review_folder: count(::Environment.in_review_folder),
             grafana_integrated_projects: count(GrafanaIntegration.enabled),
             groups: count(Group),

rubocop/rubocop-usage-data.yml

@@ -45,3 +45,4 @@ UsageData/DistinctCountByLargeForeignKey:
     - :issue_id
     - :merge_request_id
     - :merge_requests.target_project_id
+    - :agent_id

spec/factories/usage_data.rb

@@ -67,6 +67,7 @@ FactoryBot.define do
 
       # Kubernetes agents
       create(:cluster_agent, project: projects[0])
+      create(:cluster_agent_token, agent: create(:cluster_agent, project: projects[1]) )
 
       # Enabled clusters
       gcp_cluster = create(:cluster_provider_gcp, :created).cluster

spec/lib/gitlab/usage_data_spec.rb

@@ -460,7 +460,8 @@ RSpec.describe Gitlab::UsageData, :aggregate_failures do
       expect(count_data[:clusters_applications_jupyter]).to eq(1)
       expect(count_data[:clusters_applications_cilium]).to eq(1)
       expect(count_data[:clusters_management_project]).to eq(1)
-      expect(count_data[:kubernetes_agents]).to eq(1)
+      expect(count_data[:kubernetes_agents]).to eq(2)
+      expect(count_data[:kubernetes_agents_with_token]).to eq(1)
 
       expect(count_data[:deployments]).to eq(4)
       expect(count_data[:successful_deployments]).to eq(2)