Add XML files header checks

[eparovyshnaya]

Project files of xml content also must contain license headers, thus LiHo should be tought to habdle these ones.

Header comes after <?xml > instructions and all the rest is quite expectable. Here is the sample from an ArSysOp project:

<?xml version="1.0" encoding="UTF-8"?>

<!--
	Copyright (c) 2020 ArSysOp and others

	This program and the accompanying materials are made available under the
	terms of the Eclipse Public License 2.0 which is available at
	https://www.eclipse.org/legal/epl-2.0/.

	SPDX-License-Identifier: EPL-2.0

	Contributors:
		ArSysOp - initial API and implementation
-->
<feature ...