Unregister group path from apiserver when the group no longer exists

After a CRD or an APIService was deleted, the corresponding group was
never unregistered. It caused a stale entry to remain in the root path
and could potentially lead to memory leak as the groupDiscoveryHandler
was never released and the handledGroups was never cleaned up.

The commit implements the cleanup. It tracks each group's usage and
unregister the a group when there is no version for this group.

Signed-off-by: Quan Tian <qtian@vmware.com>

test/e2e/apimachinery/aggregator.go

@@ -52,6 +52,7 @@ import (
 	admissionapi "k8s.io/pod-security-admission/api"
 	samplev1alpha1 "k8s.io/sample-apiserver/pkg/apis/wardle/v1alpha1"
 	"k8s.io/utils/pointer"
+	"k8s.io/utils/strings/slices"
 
 	"github.com/onsi/ginkgo/v2"
 	"github.com/onsi/gomega"
@@ -736,6 +737,24 @@ func TestSampleAPIServer(ctx context.Context, f *framework.Framework, aggrclient
 	framework.ExpectNoError(err, "failed to count the required APIServices")
 	framework.Logf("APIService %s has been deleted.", apiServiceName)
 
+	ginkgo.By("Confirm that the group path of " + apiServiceName + " was removed from root paths")
+	groupPath := "/apis/" + apiServiceGroupName
+	err = wait.PollUntilContextTimeout(ctx, apiServiceRetryPeriod, apiServiceRetryTimeout, true, func(ctx context.Context) (done bool, err error) {
+		rootPaths := metav1.RootPaths{}
+		statusContent, err = restClient.Get().
+			AbsPath("/").
+			SetHeader("Accept", "application/json").DoRaw(ctx)
+		if err != nil {
+			return false, err
+		}
+		err = json.Unmarshal(statusContent, &rootPaths)
+		if err != nil {
+			return false, err
+		}
+		return !slices.Contains(rootPaths.Paths, groupPath), nil
+	})
+	framework.ExpectNoError(err, "Expected to not find %s from root paths", groupPath)
+
 	cleanupSampleAPIServer(ctx, client, aggrclient, n, apiServiceName)
 }