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/DownstreamService/Properties/launchSettings.json

@@ -0,0 +1,35 @@
+{
+  "iisSettings": {
+    "windowsAuthentication": false,
+    "anonymousAuthentication": true,
+    "iisExpress": {
+      "applicationUrl": "http://localhost:56411",
+      "sslPort": 0
+    }
+  },
+  "$schema": "http://json.schemastore.org/launchsettings.json",
+  "profiles": {
+    "IIS Express": {
+      "commandName": "IISExpress",
+      "launchBrowser": true,
+      "launchUrl": "api/values",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    },
+    "DownstreamService": {
+      "commandName": "Project",
+      "launchBrowser": true,
+      "launchUrl": "api/values",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      },
+      "applicationUrl": "http://localhost:5000"
+    },
+    "Docker": {
+      "commandName": "Docker",
+      "launchBrowser": true,
+      "launchUrl": "{Scheme}://{ServiceHost}:{ServicePort}/api/values"
+    }
+  }
+}