Greeting and GreetingResponse should be public (#307)

Author: slinkydeveloper

java/templates/java-maven-spring-boot/src/main/java/com/example/restatestarter/Greeter.java

@@ -16,8 +16,8 @@ public class Greeter {
   @Value("${greetingPrefix}")
   private String greetingPrefix;
 
-  record Greeting(String name) {}
-  record GreetingResponse(String message) {}
+  public record Greeting(String name) {}
+  public record GreetingResponse(String message) {}
 
   @Handler
   public GreetingResponse greet(Context ctx, Greeting req) {