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

samples/OelotKube/ApiGateway/ocelot.json

@@ -0,0 +1,20 @@
+{
+  "ReRoutes": [
+    {
+      "DownstreamPathTemplate": "/api/values",
+      "DownstreamScheme": "http",
+      "UpstreamPathTemplate": "/values",
+      "ServiceName": "downstreamservice",
+      "UpstreamHttpMethod": [ "Get" ]      
+    }
+  ],
+  "GlobalConfiguration": {
+    "ServiceDiscoveryProvider": {
+      "Host": "192.168.0.13",
+      "Port": 443,
+      "Token": "txpc696iUhbVoudg164r93CxDTrKRVWG",
+      "Namespace": "dev",
+      "Type": "kube"
+    }
+  }
+}