Add issue templates

.github/ISSUE_TEMPLATE/bug_report.md

+---
+name: Bug report
+about: Create a report to help us improve
+
+---
+
+# **Help us to keep this issue-tracker clean!  For questions or support, please refer to our [mailing lists](https://simplesamlphp.org/lists)**
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Screenshots or logs**
+If applicable, add screenshots and/or log files to help explain your problem.
+
+**Additional context**
+Add any other context about the problem here.