Add a default issue template

.gitlab/issue_templates/default.md

+## Summary
+
+(Summarize the issue encountered concisely)
+
+## Steps to reproduce
+
+(How one can reproduce the issue)
+
+## What is the current issue behaviour?
+
+(What actually happens)
+
+## What is the expected correct behaviour?
+
+(What you should see instead)
+
+## Relevant logs and/or screenshots
+
+(Paste any relevant logs/screenshots)
+
+## Possible fixes
+
+(Any ideas on how to fix the issue)