Toolchain configuration support

[kzadorozhny]

Description of the problem / feature request:

Right now platform specific kubectl and kustomize are downloaded within repository rule. This method makes support of additional operation systems or execution environments very time

Feature requests: what underlying problem are you trying to solve with this feature?

• Support additional operating systems. NixOS #54
• Support wide variety of execution environments #46
• Support symlinking system kubeconfig #22
• Running Kubernetes tests on GCP #22

Proposed design

K8sInfo = provider(
    doc = "Information about how to invoke the Kubernetes tools.",
    fields = {
        "kubectl_path": "Path to the kubectl executable.",
        "kubectl_target": "A kubectl executable target.",
        "kustomize_path": "Path to the kustomize executable.",
        "kustomize_target": "A kustomize executable target.",
        "kubeconfig_path": "Path to kubeconfig file.",
        "kubeconfig_target": "A kubeconfig file target.",
        "kubeconfig_cluster": "Kubernetes cluster name.",
        "kubeconfig_namespace": "Kubernetes namespace.",
        "kubeconfig_user": "Kubernetes user name.",
    },
)