Fix error handling in cluster_platform_configure_worker

I have also extracted an issue in
https://gitlab.com/gitlab-org/gitlab-ce/issues/53738 to surface these
errors to users but now I am just fixing the bug where
kubernetes_namespace is undefined while handling this error

app/workers/cluster_platform_configure_worker.rb

@@ -17,6 +17,6 @@ class ClusterPlatformConfigureWorker
     end
 
   rescue ::Kubeclient::HttpError => err
-    Rails.logger.error "Failed to create/update Kubernetes Namespace. id: #{kubernetes_namespace.id} message: #{err.message}"
+    Rails.logger.error "Failed to create/update Kubernetes namespace for cluster_id: #{cluster_id} with error: #{err.message}"
   end
 end

spec/workers/cluster_platform_configure_worker_spec.rb

@@ -30,4 +30,18 @@ describe ClusterPlatformConfigureWorker, '#execute' do
       described_class.new.perform(123)
     end
   end
+
+  context 'when kubeclient raises error' do
+    let(:cluster) { create(:cluster, :project) }
+
+    it 'rescues and logs the error' do
+      allow_any_instance_of(Clusters::Gcp::Kubernetes::CreateOrUpdateNamespaceService).to receive(:execute).and_raise(::Kubeclient::HttpError.new(500, 'something baaaad happened', ''))
+
+      expect(Rails.logger)
+        .to receive(:error)
+        .with("Failed to create/update Kubernetes namespace for cluster_id: #{cluster.id} with error: something baaaad happened")
+
+      described_class.new.perform(cluster.id)
+    end
+  end
 end