Added usage ping

lib/gitlab/usage_data.rb

@@ -48,6 +48,7 @@ module Gitlab
             deploy_keys: DeployKey.count,
             deployments: Deployment.count,
             environments: ::Environment.count,
+            gcp_clusters: ::Gcp::Cluster.count,
             in_review_folder: ::Environment.in_review_folder.count,
             groups: Group.count,
             issues: Issue.count,