Permit keep alive for testing grpc proxy

Author: alex268

tests/common/src/main/java/tech/ydb/test/integration/docker/GrpcProxyServer.java

@@ -4,6 +4,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.InetAddress;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 
@@ -40,6 +41,8 @@ public class GrpcProxyServer implements AutoCloseable {
     public GrpcProxyServer(ManagedChannel target, int port) {
         this.target = target;
         this.server = Grpc.newServerBuilderForPort(port, InsecureServerCredentials.create())
+                .permitKeepAliveTime(10, TimeUnit.SECONDS)
+                .permitKeepAliveWithoutCalls(true)
                 .fallbackHandlerRegistry(new ProxyRegistry())
                 .build();
         try {