Add CBOR feature gates.

For alpha, there is one apiserver feature gate and two client-go feature gates controlling
CBOR. They were initially wired to separate test-only feature gate instances in order to prevent
them from being configurable at runtime via command-line flags or environment variables (for
client-go feature gates outside of Kubernetes components). All of the integration tests required by
the KEP as alpha criteria have been implemented. This adds the feature gates to the usual feature
gate instances and removes the temporary code to support separate test-only feature gate instances.

Kubernetes-commit: 072dfcb416fd4e1ddab0a89ac4faf519e268bc96

features/features.go

@@ -18,8 +18,6 @@ package features
 
 import (
 	"errors"
-	"fmt"
-	"sync"
 	"sync/atomic"
 
 	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
@@ -143,43 +141,3 @@ var (
 	// should use AddFeaturesToExistingFeatureGates followed by ReplaceFeatureGates.
 	featureGates = &atomic.Value{}
 )
-
-// TestOnlyFeatureGates is a distinct registry of pre-alpha client features that must not be
-// included in runtime wiring to command-line flags or environment variables. It exists as a risk
-// mitigation to allow only programmatic enablement of CBOR serialization for integration testing
-// purposes.
-//
-// TODO: Once all required integration test coverage is complete, this will be deleted and the
-// test-only feature gates will be replaced by normal feature gates.
-var TestOnlyFeatureGates = &testOnlyFeatureGates{
-	features: map[Feature]bool{
-		TestOnlyClientAllowsCBOR:  false,
-		TestOnlyClientPrefersCBOR: false,
-	},
-}
-
-type testOnlyFeatureGates struct {
-	lock     sync.RWMutex
-	features map[Feature]bool
-}
-
-func (t *testOnlyFeatureGates) Enabled(feature Feature) bool {
-	t.lock.RLock()
-	defer t.lock.RUnlock()
-
-	enabled, ok := t.features[feature]
-	if !ok {
-		panic(fmt.Sprintf("test-only feature %q not recognized", feature))
-	}
-	return enabled
-}
-
-func (t *testOnlyFeatureGates) Set(feature Feature, enabled bool) error {
-	t.lock.Lock()
-	defer t.lock.Unlock()
-	if _, ok := t.features[feature]; !ok {
-		return fmt.Errorf("test-only feature %q not recognized", feature)
-	}
-	t.features[feature] = enabled
-	return nil
-}