Updated SpringBoot 2 sample to latest code

Author: sapessi

samples/springboot2/pet-store/src/main/java/com/amazonaws/serverless/sample/springboot2/Application.java

@@ -21,7 +21,7 @@
 
 @SpringBootApplication
 @Import({ PetsController.class })
-public class Application extends SpringBootServletInitializer {
+public class Application {
 
     // silence console logging
     @Value("${logging.level.root:OFF}")

samples/springboot2/pet-store/src/main/java/com/amazonaws/serverless/sample/springboot2/StreamLambdaHandler.java

@@ -25,6 +25,14 @@ public class StreamLambdaHandler implements RequestStreamHandler {
         try {
             handler = SpringBootLambdaContainerHandler.getAwsProxyHandler(Application.class);
 
+            // For applications that take longer than 10 seconds to start, use the async builder:
+            // long startTime = Instant.now().toEpochMilli();
+            // handler = new SpringBootProxyHandlerBuilder()
+            //                    .defaultProxy()
+            //                    .asyncInit(startTime)
+            //                    .springBootApplication(Application.class)
+            //                    .buildAndInitialize();
+
             // we use the onStartup method of the handler to register our custom filter
             handler.onStartup(servletContext -> {
                 FilterRegistration.Dynamic registration = servletContext.addFilter("CognitoIdentityFilter", CognitoIdentityFilter.class);