Kubectl delete label support

[Mert18]

Describe the bug
Kubectl.label() does not have a delete option as far as I have seen. Normally in k8s, a label can be deleted via CLI by putting "-" at the end of the label.

Ex:
kubectl label node <nodename> <labelname>=labelvalue adds the label, and
kubectl label node <nodename> <labelname>- deletes the label

But in Kubectl.label() function cannot have "-" at the end of the label name due to some restrictions. Can it be achieved?

By the way, I found a getaround with the jsonpatches and created a patch to the resource in order to achieve this functionality:

String patchString = "[{ \"op\": \"remove\", \"path\": \"/labelpath\" }]";
                V1Patch patch = new V1Patch(patchString);
                Kubectl.patch(V1Node.class).apiClient(apiClient).name(nodeName).patchContent(patch).execute();

[brendandburns]

We'd be happy to take a PR to add support for this in the KubectlLabel class.

[shubhbapna]

Hi there, first time contributor here. Can I take a crack at this issue?

[shubhbapna]

Seems like to behind the scenes to remove a label kubectl makes a patch where it sets the label key as null to delete it like this

Request Body: {"metadata":{"labels":{"foo":null}}}
curl -v -XPATCH  -H "Content-Type: application/merge-patch+json" -H "User-Agent: kubectl/4.10.0" -H "Accept: application/json" 'https://<host>/api/v1/nodes/minikube?fieldManager=kubectl-label'

So I can simply add a method in KubectlLabel like this

public KubectlLabel<ApiType> deleteLabel(String key) {
    this.addingLabels.put(key, null);
    return this;
}

Wdyt?

[shubhbapna]

/assign

[LUEDDEA]

@shubhbapna
that is more or less, what I already do in my solution using the existing library as is:
label(V1Node.class).apiClient(client).name(nodeName).addLabel(key, null).execute();

[shubhbapna]

Yeah, maybe for the sake of clarity since we are using addLabel to well delete a label, we can add this simple deleteLabel method?