Add copyrights file to the arduino-app-cli and router .deb packages

Co-authored-by: Luca Rinaldi <lucarin@protonmail.com>
Co-authored-by: Alessio Perugini <alessio@perugini.xyz>

Author: 3 people

debian/arduino-router/usr/share/doc/arduino-router/copyright

@@ -0,0 +1,12 @@
+Copyright 2025 ARDUINO SA (http://www.arduino.cc/)
+
+This software is released under the GNU General Public License version 3,
+which covers the main part of arduino-router.
+The terms of this license can be found at:
+https://www.gnu.org/licenses/gpl-3.0.en.html
+
+You can be released from the requirements of the above licenses by purchasing
+a commercial license. Buying such a license is mandatory if you want to
+modify or otherwise use the software for commercial activities involving the
+Arduino software without disclosing the source code of your own applications.
+To purchase a commercial license, send an email to license@arduino.cc.