Support expiry_seconds parameter on kubeconfig requests

[andrewsomething]

The /v2/kubernetes/clusters/$K8S_CLUSTER_ID/kubeconfig endpoint supports an expiry_seconds query paramater:

https://developers.digitalocean.com/documentation/v2/#retrieve-the-kubeconfig-for-a-kubernetes-cluster

godo does not currently support passing that parameter:

godo/kubernetes.go

Line 516 in b6eed88

func (svc *KubernetesServiceOp) GetKubeConfig(ctx context.Context, clusterID string) (*KubernetesClusterConfig, *Response, error) {

In order to keep the API stable for callers of the existing method, a new method should be added (e.g. GetKubeConfigWithExpiry).

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This is to enable a doctl feature request. Adding here to track the needed work all the way through. See: digitalocean/doctl#791

[ivanlemeshev]

Hey @andrewsomething I would like to do this issue

[andrewsomething]

@ivanlemeshev Go for it! Don't hesitate to ask, if you have any questions.

[andrewsomething]

Closed via #382