Add some additional doc to HeaderConfig#methods()

Fixes #46897

Author: gsmet

extensions/vertx-http/runtime/src/main/java/io/quarkus/vertx/http/runtime/HeaderConfig.java

@@ -21,7 +21,9 @@ public interface HeaderConfig {
     String value();
 
     /**
-     * The HTTP methods for this header configuration
+     * The HTTP methods for this header configuration.
+     * <p>
+     * If no HTTP methods are specified, the header will be always added.
      */
     Optional<List<String>> methods();
 }