Make spring-task-launch-request-function as auto-config

* Also make a `spring-spel-function`, `spring-filter-function` as auto-config
* Fix Checkstyle violations in those module, as well as in the `spring-payload-converter-function`

function/spring-payload-converter-function/src/main/java/functions/ByteArrayTextToString.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2020 the original author or authors.
+ * Copyright 2020-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,6 +24,8 @@ import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.util.MimeTypeUtils;
 
 /**
+ * The function which transforms a byte array to string.
+ *
  * @author Christian Tzolov
  */
 public class ByteArrayTextToString implements Function<Message<?>, Message<?>> {

function/spring-payload-converter-function/src/main/java/functions/package-info.java

@@ -0,0 +1,4 @@
+/**
+ * The utility functions for common usage.
+ */
+package functions;