move templates to .github

.github/issue_template.md

@@ -0,0 +1,22 @@
+Thank you very much for your interest in TetGen! Reporting your issue here helps to improve the code.
+
+### Legal
+By opening this issue, you agree to the terms of the contributor license agreement stated in [CONTRIBUTING.md](https://codeberg.org/TetGen/TetGen/src/branch/main/CONTRIBUTING.md)
+
+### Kind of issue (bug, feature request...):
+
+### Issue description:
+
+### Expected behavior: 
+
+### Observed behavior: 
+
+### Environment:
+   - TeGen version:
+   - OS (e.g. MacOS 14):
+   - Architecture (e.g. x64, aarch64):
+   - Compiler vendor + version:
+
+### Minimum working example:
+
+Please attach input data which allow to reproduce the problem.