Add @Configuration on @Enable*-annotated classes

reactive/webflux/java/hello-security-explicit/src/main/java/example/SecurityConfiguration.java

@@ -17,6 +17,7 @@
 package example;
 
 import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
 import org.springframework.security.config.annotation.web.reactive.EnableWebFluxSecurity;
 import org.springframework.security.config.web.server.ServerHttpSecurity;
 import org.springframework.security.core.userdetails.MapReactiveUserDetailsService;
@@ -32,6 +33,7 @@ import static org.springframework.security.config.Customizer.withDefaults;
  * @author Rob Winch
  * @since 5.0
  */
+@Configuration
 @EnableWebFluxSecurity
 public class SecurityConfiguration {