chore(github): add issue templates

relates to STACKITTPR-138

Author: rubenhoenle

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,35 @@
+---
+name: Bug report
+about: Report a bug in the STACKIT CLI
+title: ''
+labels: bug
+assignees: ''
+
+---
+
+## Description
+
+*Please add a clear and concise description of what the bug is.*
+
+## Steps to reproduce
+<!-- Please provide us with the steps to reproduce the behavior. -->
+
+1. Run `stackit ...`
+2. Run `stackit ...`
+3. ...
+
+## Actual behavior
+
+*Please describe the current behavior of the STACKIT CLI. Don't forget to add detailed information like error messages.*
+
+## Expected behavior
+
+*Please describe the behavior which you would expect from the STACKIT CLI in that case.*
+
+## Environment
+ - OS: 
+ - Version of STACKIT CLI (see `stackit --version`): `vX.X.X`
+
+**Additional information**
+
+*Feel free to add any additional information here*