[feature request] support for --kube-context

[rustielin]

Typical helm commands let the user specify --kube-context for a specific context in the kubeconfig.

There seems to be a workaround by specifying the environment variable HELM_KUBECONTEXT for helm under the hood (https://helm.sh/docs/helm/helm/), but having an explicit option in helm diff would be ideal and easier to discover.