Introduce MultiCIDRRangeAllocator

MultiCIDRRangeAllocator is a new Range Allocator which makes using
multiple ClusterCIDRs possible. It consists of two controllers, one for
reconciling the ClusterCIDR API objects and the other for allocating
Pod CIDRs to the nodes.

The allocation is based on the rules defined in
https://github.com/kubernetes/enhancements/tree/master/keps/sig-network/2593-multiple-cluster-cidrs

cmd/cloud-controller-manager/.import-restrictions

@@ -39,4 +39,5 @@ rules:
       - k8s.io/kubernetes/pkg/util/taints
       - k8s.io/kubernetes/pkg/proxy/util
       - k8s.io/kubernetes/pkg/proxy/util/testing
+      - k8s.io/kubernetes/pkg/util/slice
       - k8s.io/kubernetes/pkg/util/sysctl

cmd/cloud-controller-manager/nodeipamcontroller.go

@@ -26,6 +26,8 @@ import (
 	"net"
 	"strings"
 
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
+	"k8s.io/client-go/informers/networking/v1alpha1"
 	cloudprovider "k8s.io/cloud-provider"
 	"k8s.io/cloud-provider/app"
 	cloudcontrollerconfig "k8s.io/cloud-provider/app/config"
@@ -36,6 +38,7 @@ import (
 	nodeipamcontroller "k8s.io/kubernetes/pkg/controller/nodeipam"
 	nodeipamconfig "k8s.io/kubernetes/pkg/controller/nodeipam/config"
 	"k8s.io/kubernetes/pkg/controller/nodeipam/ipam"
+	"k8s.io/kubernetes/pkg/features"
 	netutils "k8s.io/utils/net"
 )
 
@@ -120,8 +123,14 @@ func startNodeIpamController(initContext app.ControllerInitContext, ccmConfig *c
 		return nil, false, err
 	}
 
+	var clusterCIDRInformer v1alpha1.ClusterCIDRInformer
+	if utilfeature.DefaultFeatureGate.Enabled(features.MultiCIDRRangeAllocator) {
+		clusterCIDRInformer = ctx.InformerFactory.Networking().V1alpha1().ClusterCIDRs()
+	}
+
 	nodeIpamController, err := nodeipamcontroller.NewNodeIpamController(
 		ctx.InformerFactory.Core().V1().Nodes(),
+		clusterCIDRInformer,
 		cloud,
 		ctx.ClientBuilder.ClientOrDie(initContext.ClientName),
 		clusterCIDRs,