Add DisableCloudProviders FG

FeatureGate acts as a secondary switch to disable cloud-controller loops
in KCM, Kubelet and KAPI.

Provide comprehensive logging information to users, so they will be
guided in adoption of out-of-tree cloud provider implementation.

cmd/kube-controller-manager/app/cloudproviders.go

@@ -19,7 +19,9 @@ package app
 import (
 	"fmt"
 
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	"k8s.io/klog/v2"
+	"k8s.io/kubernetes/pkg/features"
 
 	"k8s.io/client-go/informers"
 	cloudprovider "k8s.io/cloud-provider"
@@ -32,6 +34,14 @@ func createCloudProvider(cloudProvider string, externalCloudVolumePlugin string,
 	var cloud cloudprovider.Interface
 	var loopMode ControllerLoopMode
 	var err error
+
+	if utilfeature.DefaultFeatureGate.Enabled(features.DisableCloudProviders) && cloudprovider.IsDeprecatedInternal(cloudProvider) {
+		cloudprovider.DisableWarningForProvider(cloudProvider)
+		return nil, ExternalLoops, fmt.Errorf(
+			"cloud provider %q was specified, but built-in cloud providers are disabled. Please set --cloud-provider=external and migrate to an external cloud provider",
+			cloudProvider)
+	}
+
 	if cloudprovider.IsExternal(cloudProvider) {
 		loopMode = ExternalLoops
 		if externalCloudVolumePlugin == "" {