Add a Prometheus handler. (#591)

* Add a Prometheus handler.

* Address comments

examples/prometheus/Prometheus.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Net.Http;
+using System.Threading;
+using k8s;
+using k8s.Monitoring;
+using Prometheus;
+
+namespace prom
+{
+    internal class Prometheus
+    {
+        private static void Main(string[] args)
+        {
+            var config = KubernetesClientConfiguration.BuildDefaultConfig();
+            var handler = new PrometheusHandler();
+            IKubernetes client = new Kubernetes(config, new DelegatingHandler[] { handler });
+
+            var server = new MetricServer(hostname: "localhost", port: 1234);
+            server.Start();
+
+            Console.WriteLine("Making requests!");
+            while (true)
+            {
+                client.ListNamespacedPod("default");
+                client.ListNode();
+                client.ListNamespacedDeployment("default");
+                Thread.Sleep(1000);
+            }
+        }
+    }
+}

examples/prometheus/prometheus.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\KubernetesClient\KubernetesClient.csproj" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net5</TargetFramework>
+  </PropertyGroup>
+
+</Project>