Add Kubernetes healthcheck

[CarlosLanderas]

New Kubernetes HealthCheck with initial support for Deployments, Pods and Services.
Good to monitor your Asp.Net application dependencies that are running within a k8s cluster.

This healthcheck is also good for configuring a HealthChecks UI interface to verify cluster status like nagios does.

All Checks can configure a condition against V1Deployment, V1Pod and V1Service so you can practically configure whatever condition with the k8s API returned object. (Spec, Metadata, Status, etc...)

Below there are some samples configuring conditions like desired replicas and ready replicas, checking the configured type for a service or confirming that a given pod has the target configured label.
But you could configure all kind of checks to meet your criteria.

Sample with configuration using .kubeconfig

  services
    .AddHealthChecks()
    .AddKubernetes(setup =>
     {
      setup.WithConfiguration(k8s.KubernetesClientConfiguration.BuildConfigFromConfigFile())
       .CheckDeployment("wordpress-one-wordpress",
                  d => d.Status.Replicas == 2 && d.Status.ReadyReplicas == 2)
       .CheckService("wordpress-one-wordpress", s => s.Spec.Type == "LoadBalancer")
       .CheckPod("myapp-pod", p => p.Metadata.Labels["app"] == "myapp");
     });

Sample configuring a remote AKS Cluster:

services
.AddHealthChecks()
.AddKubernetes(setup =>
    {
    setup.WithConfiguration(new KubernetesClientConfiguration
      {
        Host = "https://my-aks-cluster.westeurope.azmk8s.io:443",
        SkipTlsVerify = true,
        AccessToken = "youraccesstoken"
      })
     .CheckDeployment("wordpress-one-wordpress",
               d => d.Status.Replicas == 2 && d.Status.ReadyReplicas == 2)
     .CheckService("wordpress-one-wordpress", s => s.Spec.Type == "LoadBalancer")
     .CheckPod("myapp-pod", p => p.Metadata.Labels["app"] == "myapp");
});

[CarlosLanderas]

@unaizorrilla did you have time to review this? I know.some people that.would use it as soon as published