Add popular open-source license templates

Add eight license templates:
- Apache2.txt: Apache License 2.0
- BSD2.txt: BSD 2-Clause License
- BSD3.txt: BSD 3-Clause License
- GPLv2.txt: GNU General Public License v2
- ISC.txt: ISC License
- LGPL.txt: GNU Lesser General Public License v3
- MIT0.txt: MIT No Attribution License (0-Clause MIT)
- MPL2.txt: Mozilla Public License v2.0
- Unlicense.txt: Unlicense (public domain)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

licenses/GPLv2.txt

@@ -0,0 +1,18 @@
+GNU GENERAL PUBLIC LICENSE
+Version 2, June 1991
+
+Copyright (c) YEAR AUTHOR
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.