Add license header to gradle files (#2)

* Add license header to gradle files

* Remove license header from gradle-wrapper.properties

Author: wei-qiang

build.gradle

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: Contributors to the Power Grid Model project <powergridmodel@lfenergy.org>
+//
+// SPDX-License-Identifier: MPL-2.0
+
 import javax.inject.Inject
 
 plugins {

gradle.properties

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: Contributors to the Power Grid Model project <powergridmodel@lfenergy.org>
+#
+# SPDX-License-Identifier: MPL-2.0
+
 #jextract_bin=fill_in_when_to_use_local_jextract
 
 #URL Jextract java version 25

settings.gradle

@@ -1 +1,5 @@
+// SPDX-FileCopyrightText: Contributors to the Power Grid Model project <powergridmodel@lfenergy.org>
+//
+// SPDX-License-Identifier: MPL-2.0
+
 rootProject.name = 'jpgm'