chore(github): add issue templates (#750)

relates to STACKITTPR-138

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,33 @@
+---
+name: Feature request
+about: Suggest an idea for the STACKIT Terraform provider
+title: ''
+labels: enhancement
+assignees: ''
+
+---
+
+## Problem description
+
+*Is your feature request related to a problem? If so, please give us a clear and concise description of what the problem is. 
+Example: I'm always frustrated when [...]*
+
+## Proposed solution
+
+*A clear and concise description of what you want to happen.*
+
+<!-- Please add an example terraform config below which helps us understand your proposed solution. -->
+
+```terraform
+# put your terraform example here
+# ...
+```
+
+## Alternative solutions (optional)
+
+*A clear and concise description of any alternative solutions or features you've considered. (optional)*
+
+## Additional information
+
+*Feel free to add any additional information here.*
+