Use connection pool for http communications with extension.

Author: purple4reina

dd-trace-core/src/main/java/datadog/trace/lambda/LambdaHandler.java

@@ -15,6 +15,7 @@
 import java.io.ByteArrayInputStream;
 import java.nio.charset.StandardCharsets;
 import java.util.Base64;
+import okhttp3.ConnectionPool;
 import okhttp3.MediaType;
 import okhttp3.OkHttpClient;
 import okhttp3.Request;
@@ -57,6 +58,7 @@ public class LambdaHandler {
           .writeTimeout(REQUEST_TIMEOUT_IN_S, SECONDS)
           .readTimeout(REQUEST_TIMEOUT_IN_S, SECONDS)
           .callTimeout(REQUEST_TIMEOUT_IN_S, SECONDS)
+          .connectionPool(new ConnectionPool(5, 300, SECONDS))
           .build();
 
   private static final MediaType jsonMediaType = MediaType.parse("application/json");