Fix copyrights and licenses headers in XML file

SPDX comments need to be after `<?xml version="1.0" encoding="UTF-8"?>` in XML files.

rules.xml

+<?xml version="1.0" encoding="UTF-8"?>
+
 <!--
 SPDX-FileCopyrightText: 2021 OW2
 
 SPDX-License-Identifier: Apache-2.0
 -->
 
-<?xml version="1.0" encoding="UTF-8"?>
 <ruleset comparisonMethod="maven"
          xmlns="http://mojo.codehaus.org/versions-maven-plugin/rule/2.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://mojo.codehaus.org/versions-maven-plugin/rule/2.0.0 https://www.mojohaus.org/versions-maven-plugin/xsd/rule-2.0.0.xsd">

webapp/src/main/webapp/WEB-INF/web.xml

+<?xml version="1.0" encoding="UTF-8"?>
+
 <!--
 SPDX-FileCopyrightText: 2021 OW2
 
 SPDX-License-Identifier: Apache-2.0
 -->
 
-<?xml version="1.0" encoding="UTF-8"?>
 <web-app
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         version="3.1"