Add declarative default for RC.Spec.Replicas

Remove manual default:

```
$ git diff
diff --git a/pkg/apis/core/v1/defaults.go b/pkg/apis/core/v1/defaults.go
index e66de8bb432..1dd28dd35fb 100644
--- a/pkg/apis/core/v1/defaults.go
+++ b/pkg/apis/core/v1/defaults.go
@@ -60,10 +60,6 @@ func SetDefaults_ReplicationController(obj *v1.ReplicationController) {
                        obj.Labels = labels
                }
        }
-       if obj.Spec.Replicas == nil {
-               obj.Spec.Replicas = new(int32)
-               *obj.Spec.Replicas = 1
-       }
 }
 func SetDefaults_Volume(obj *v1.Volume) {
        if ptr.AllPtrFieldsNil(&obj.VolumeSource) {
```

The test fails:

```
$ go test ./pkg/apis/core/v1 | grep -v gate | grep -v SetEmulationVersion
--- FAIL: TestSetDefaultReplicationControllerReplicas (0.00s)
    defaults_test.go:1608: expected: 1 replicas, got: 0
FAIL
FAIL	k8s.io/kubernetes/pkg/apis/core/v1	0.269s
FAIL
```

Declare the default, update codegen and re-run the test:

```
$ git diff
diff --git a/staging/src/k8s.io/api/core/v1/types.go b/staging/src/k8s.io/api/core/v1/types.go
index 406ab56a002..7e5136fe9f6 100644
--- a/staging/src/k8s.io/api/core/v1/types.go
+++ b/staging/src/k8s.io/api/core/v1/types.go
@@ -5101,6 +5101,7 @@ type ReplicationControllerSpec struct {
        // Defaults to 1.
        // More info: https://kubernetes.io/docs/concepts/workloads/controllers/replicationcontroller#what-is-a-replicationcontroller
        // +optional
+       // +default=1
        // +k8s:minimum=0
        Replicas *int32 `json:"replicas,omitempty" protobuf:"varint,1,opt,name=replicas"`

$ ./hack/update-codegen.sh default
+++ [1219 08:58:43] Generating defaulter code for 102 targets

$ git diff
diff --git a/pkg/apis/core/v1/zz_generated.defaults.go b/pkg/apis/core/v1/zz_generated.defaults.go
index 3b6eb4f0a93..567c49053aa 100644
--- a/pkg/apis/core/v1/zz_generated.defaults.go
+++ b/pkg/apis/core/v1/zz_generated.defaults.go
@@ -878,6 +878,10 @@ func SetObjectDefaults_PodTemplateList(in *corev1.PodTemplateList) {

 func SetObjectDefaults_ReplicationController(in *corev1.ReplicationController) {
        SetDefaults_ReplicationController(in)
+       if in.Spec.Replicas == nil {
+               var ptrVar1 int32 = 1
+               in.Spec.Replicas = &ptrVar1
+       }
        if in.Spec.Template != nil {
                SetDefaults_PodSpec(&in.Spec.Template.Spec)
                for i := range in.Spec.Template.Spec.Volumes {

$ go test ./pkg/apis/core/v1 | grep -v gate | grep -v SetEmulationVersion
ok  	k8s.io/kubernetes/pkg/apis/core/v1	(cached)
```

api/openapi-spec/v3/api__v1_openapi.json

@@ -6528,6 +6528,7 @@
             "type": "integer"
           },
           "replicas": {
+            "default": 1,
             "description": "Replicas is the number of desired replicas. This is a pointer to distinguish between explicit zero and unspecified. Defaults to 1. More info: https://kubernetes.io/docs/concepts/workloads/controllers/replicationcontroller#what-is-a-replicationcontroller",
             "format": "int32",
             "type": "integer"

pkg/apis/core/v1/defaults.go

@@ -60,10 +60,7 @@ func SetDefaults_ReplicationController(obj *v1.ReplicationController) {
 			obj.Labels = labels
 		}
 	}
-	if obj.Spec.Replicas == nil {
-		obj.Spec.Replicas = new(int32)
-		*obj.Spec.Replicas = 1
-	}
+	// obj.Spec.Replicas is defaulted declaratively
 }
 func SetDefaults_Volume(obj *v1.Volume) {
 	if ptr.AllPtrFieldsNil(&obj.VolumeSource) {

pkg/apis/core/v1/zz_generated.defaults.go

@@ -878,6 +878,10 @@ func SetObjectDefaults_PodTemplateList(in *corev1.PodTemplateList) {
 
 func SetObjectDefaults_ReplicationController(in *corev1.ReplicationController) {
 	SetDefaults_ReplicationController(in)
+	if in.Spec.Replicas == nil {
+		var ptrVar1 int32 = 1
+		in.Spec.Replicas = &ptrVar1
+	}
 	if in.Spec.Template != nil {
 		SetDefaults_PodSpec(&in.Spec.Template.Spec)
 		for i := range in.Spec.Template.Spec.Volumes {

pkg/generated/openapi/zz_generated.openapi.go

@@ -30098,6 +30098,7 @@ func schema_k8sio_api_core_v1_ReplicationControllerSpec(ref common.ReferenceCall
 					"replicas": {
 						SchemaProps: spec.SchemaProps{
 							Description: "Replicas is the number of desired replicas. This is a pointer to distinguish between explicit zero and unspecified. Defaults to 1. More info: https://kubernetes.io/docs/concepts/workloads/controllers/replicationcontroller#what-is-a-replicationcontroller",
+							Default:     1,
 							Type:        []string{"integer"},
 							Format:      "int32",
 						},

staging/src/k8s.io/api/core/v1/generated.proto

@@ -5085,6 +5085,7 @@ message ReplicationControllerSpec {
   // Defaults to 1.
   // More info: https://kubernetes.io/docs/concepts/workloads/controllers/replicationcontroller#what-is-a-replicationcontroller
   // +optional
+  // +default=1
   // +k8s:minimum=0
   optional int32 replicas = 1;
 

staging/src/k8s.io/api/core/v1/types.go

@@ -5107,6 +5107,7 @@ type ReplicationControllerSpec struct {
 	// Defaults to 1.
 	// More info: https://kubernetes.io/docs/concepts/workloads/controllers/replicationcontroller#what-is-a-replicationcontroller
 	// +optional
+	// +default=1
 	// +k8s:minimum=0
 	Replicas *int32 `json:"replicas,omitempty" protobuf:"varint,1,opt,name=replicas"`
 

staging/src/k8s.io/client-go/applyconfigurations/internal/internal.go

@@ -7649,6 +7649,7 @@ var schemaYAML = typed.YAMLObject(`types:
     - name: replicas
       type:
         scalar: numeric
+      default: 1
     - name: selector
       type:
         map: