features: add UserNamespacesSupport feature

define a feature gate for the user namespaces support.  The feature is
not enabled by default.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/features/kube_features.go

@@ -813,6 +813,13 @@ const (
 	// Enable resource managers to make NUMA aligned decisions
 	TopologyManager featuregate.Feature = "TopologyManager"
 
+	// owner: @rata, @giuseppe
+	// kep: http://kep.k8s.io/127
+	// alpha: v1.25
+	//
+	// Enables user namespace support for stateless pods.
+	UserNamespacesStatelessPodsSupport featuregate.Feature = "UserNamespacesStatelessPodsSupport"
+
 	// owner: @cofyc
 	// alpha: v1.21
 	VolumeCapacityPriority featuregate.Feature = "VolumeCapacityPriority"
@@ -1071,6 +1078,8 @@ var defaultKubernetesFeatureGates = map[featuregate.Feature]featuregate.FeatureS
 
 	VolumeCapacityPriority: {Default: false, PreRelease: featuregate.Alpha},
 
+	UserNamespacesStatelessPodsSupport: {Default: false, PreRelease: featuregate.Alpha},
+
 	WinDSR: {Default: false, PreRelease: featuregate.Alpha},
 
 	WinOverlay: {Default: true, PreRelease: featuregate.Beta},