docs: add missing license header

directory-upload/src/main/resources/META-INF/resources/frontend/directory-upload/directory-upload-mixin.js

@@ -1,3 +1,16 @@
+/*
+ * Copyright 2024 Vaadin Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
 import '@vaadin/upload/src/vaadin-upload-mixin.js';
 import '@vaadin/upload/src/vaadin-upload-file-list-mixin.js';
 import { Debouncer } from '@vaadin/component-base/src/debounce.js';