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/Controllers/ValuesController.cs

@@ -0,0 +1,45 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+
+namespace DownstreamService.Controllers
+{
+    [Route("api/[controller]")]
+    [ApiController]
+    public class ValuesController : ControllerBase
+    {
+        // GET api/values
+        [HttpGet]
+        public ActionResult<IEnumerable<string>> Get()
+        {
+            return new string[] { "value1", "value2" };
+        }
+
+        // GET api/values/5
+        [HttpGet("{id}")]
+        public ActionResult<string> Get(int id)
+        {
+            return "value";
+        }
+
+        // POST api/values
+        [HttpPost]
+        public void Post([FromBody] string value)
+        {
+        }
+
+        // PUT api/values/5
+        [HttpPut("{id}")]
+        public void Put(int id, [FromBody] string value)
+        {
+        }
+
+        // DELETE api/values/5
+        [HttpDelete("{id}")]
+        public void Delete(int id)
+        {
+        }
+    }
+}