Add http2 keep alive in watch (#781)

Author: zhiweiv

src/KubernetesClient/Kubernetes.ConfigInit.cs

@@ -192,7 +192,12 @@ private void CreateHttpClient(DelegatingHandler[] handlers, KubernetesClientConf
                 //
                 // Should remove after better solution
 
-                var sh = new SocketsHttpHandler();
+                var sh = new SocketsHttpHandler
+                {
+                    KeepAlivePingPolicy = HttpKeepAlivePingPolicy.WithActiveRequests,
+                    KeepAlivePingDelay = TimeSpan.FromMinutes(3),
+                    KeepAlivePingTimeout = TimeSpan.FromSeconds(30),
+                };
                 sh.ConnectCallback = async (context, token) =>
                 {
                     var socket = new Socket(SocketType.Stream, ProtocolType.Tcp)