Add a example for union operator in the shell env (#16282)

In the current example, single quotes are used, but the union operator can  be confusing.
Incorrect：
`kubectl get pod -o=jsonpath='{.items[*]['metadata.name','spec.nodeName']}'`  
Correct:
`kubectl get pods -o=jsonpath="{.items[*]['metadata.name', 'status.capacity']}"`

content/en/docs/reference/kubectl/jsonpath.md

@@ -85,6 +85,7 @@ kubectl get pods -o json
 kubectl get pods -o=jsonpath='{@}'
 kubectl get pods -o=jsonpath='{.items[0]}'
 kubectl get pods -o=jsonpath='{.items[0].metadata.name}'
+kubectl get pods -o=jsonpath="{.items[*]['metadata.name', 'status.capacity']}"
 kubectl get pods -o=jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.startTime}{"\n"}{end}'
 ```