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)
```

Kubernetes-commit: 21b3da7e5aadf77e8fd17e467c86ff7e18f7d9ed

applyconfigurations/internal/internal.go

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