CHORE: add gitlab issue template

Refs: #3

.gitlab/issue_templates/Bug.md

+## Steps to reproduce
+
+(How one can reproduce the issue - this is very important)
+
+## What is the current *bug* behavior?
+
+(What actually happens)
+
+## What is the expected *correct* behavior?
+
+(What you should see instead)
+
+## Relevant logs and/or screenshots
+
+(Paste any relevant logs - please use code blocks (```) to format console output,
+logs, and code as it's very hard to read otherwise.)
+
+## Possible fixes
+
+(If you can, link to the line of code that might be responsible for the problem)
+
+/label ~BUG