kubernetes provider (#772)

* feat: Kubernetes ServiceDiscoveryProvider

* 编写k8s测试例子

* feat：fix kube config

* feat： remove port

* feat ： complete the k8s test

* feat :  add kubeserviceDiscovery test

* feat : add kube provider unittest

* feat :add kubetnetes docs

how to use ocelot with kubetnetes docs

* keep the configuration as simple as possible, no qos, no cache

* fix: use http

* add PollingKubeServiceDiscovery

* feat : refactor logger

* feat : add  pollkube docs

* feat：Remove unnecessary code

* feat ： code-block json

src/Ocelot.Provider.Kubernetes/KubernetesProviderFactory.cs

@@ -0,0 +1,38 @@
+using KubeClient;
+using Microsoft.Extensions.DependencyInjection;
+using Ocelot.Logging;
+using Ocelot.ServiceDiscovery;
+using System;
+
+namespace Ocelot.Provider.Kubernetes
+{
+    public static class KubernetesProviderFactory
+    {
+        public static ServiceDiscoveryFinderDelegate Get = (provider, config, name) =>
+        {
+            var factory = provider.GetService<IOcelotLoggerFactory>();             
+            return GetkubeProvider(provider, config, name, factory); 
+        };
+
+        private static ServiceDiscovery.Providers.IServiceDiscoveryProvider GetkubeProvider(IServiceProvider provider, Configuration.ServiceProviderConfiguration config, string name, IOcelotLoggerFactory factory)
+        {
+            var kubeClientFactory = provider.GetService<IKubeApiClientFactory>();
+            var k8sRegistryConfiguration = new KubeRegistryConfiguration()
+            {
+                ApiEndPoint = new Uri($"https://{config.Host}:{config.Port}"),
+                KeyOfServiceInK8s = name,
+                KubeNamespace = config.Namesapce,
+                AuthStrategy = KubeAuthStrategy.BearerToken,
+                AccessToken = config.Token,
+                AllowInsecure = true // Don't validate server certificate
+            };
+
+            var k8sServiceDiscoveryProvider = new Kube(k8sRegistryConfiguration, factory, kubeClientFactory);
+            if (config.Type?.ToLower() == "pollkube")
+            {
+                return new PollKube(config.PollingInterval, factory, k8sServiceDiscoveryProvider);
+            }
+            return k8sServiceDiscoveryProvider;
+        }
+    }
+}