Merge pull request #34020 from juanvallejo/jvallejo/allow-empty-annotation-values

Automatic merge from submit-queue

Allow empty annotation values

Related downstream issue: https://github.com/openshift/origin/issues/11175

**Release note**:
```release-note
release-note-none
```

Annotations with empty values can be used, for example, in diagnostics
logging. This patch removes the client-side check for empty values in
an annotation key-value pair.

**Before**
```
$ kubectl annotate pod zookeeper-1 node-selector="" --overwrite
error: invalid annotation format: node-selector=
```

**After**
```
$ kubectl annotate pod zookeeper-1 node-selector="" --overwrite
pod "zookeper-1" annotated
```

```
$ kubectl get po/zookeeper-1 --template='{{.metadata.annotations}}'
map[... node-selector: test-label:test]
```

@fabianofranz @liggitt

pkg/kubectl/cmd/label.go

@@ -122,7 +122,7 @@ func parseLabels(spec []string) (map[string]string, []string, error) {
 	for _, labelSpec := range spec {
 		if strings.Index(labelSpec, "=") != -1 {
 			parts := strings.Split(labelSpec, "=")
-			if len(parts) != 2 || len(parts[1]) == 0 {
+			if len(parts) != 2 {
 				return nil, nil, fmt.Errorf("invalid label spec: %v", labelSpec)
 			}
 			if errs := validation.IsValidLabelValue(parts[1]); len(errs) != 0 {