Call ClusterPlatformConfigureWorker to re-use code

We remove configure_project_service_account and replace
ClusterPlatformConfigureWorker as they perform exactly the same piece of
work. This also makes GKE cluster creation to be the same as Adding
existing cluster - they both now use another worker to execute
CreateOrUpdateNamespaceService.

app/services/clusters/gcp/finalize_creation_service.rb

@@ -12,7 +12,8 @@ module Clusters
         create_gitlab_service_account!
         configure_kubernetes
         cluster.save!
-        configure_project_service_account
+
+        ClusterPlatformConfigureWorker.perform_async(cluster.id)
 
       rescue Google::Apis::ServerError, Google::Apis::ClientError, Google::Apis::AuthorizationError => e
         provider.make_errored!("Failed to request to CloudPlatform; #{e.message}")
@@ -55,15 +56,6 @@ module Clusters
         ).execute
       end
 
-      def configure_project_service_account
-        kubernetes_namespace = cluster.find_or_initialize_kubernetes_namespace(cluster.cluster_project)
-
-        Clusters::Gcp::Kubernetes::CreateOrUpdateNamespaceService.new(
-          cluster: cluster,
-          kubernetes_namespace: kubernetes_namespace
-        ).execute
-      end
-
       def authorization_type
         create_rbac_cluster? ? 'rbac' : 'abac'
       end

spec/services/clusters/gcp/finalize_creation_service_spec.rb

@@ -48,6 +48,12 @@ describe Clusters::Gcp::FinalizeCreationService, '#execute' do
       expect(kubernetes_namespace.service_account_name).to eq("#{namespace}-service-account")
       expect(kubernetes_namespace.service_account_token).to be_present
     end
+
+    it 'calls ClusterPlatformConfigureWorker in a ascync fashion' do
+      expect(ClusterPlatformConfigureWorker).to receive(:perform_async).with(cluster.id)
+
+      subject
+    end
   end
 
   shared_examples 'error' do