[gitlab] Add templates for issues and MR

These template should be used when opening a new issue or merge
request.

There are two templates under issue:
- Default.md which is a bug report
- suggestion.md which is for suggestion to be implemented

To use them, select the corresponding template in the dropdown
beside the title of the issue/merge request.

Only available once merge in the default branch.

.gitlab/issue_templates/Default.md

+Summary
+
+(Summarize the bug encountered concisely)
+
+
+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)

.gitlab/issue_templates/suggestion.md

+Summary
+
+(Summarize the suggestion concisely)
+
+
+What does it provide ?
+
+(What is the goal of this suggestion)
+
+
+Why is it needed ?
+
+(Explain the motivation of the suggestion)
+
+
+Relevant links / references
+
+(Paste any relevant links / image for the implementation of the suggestion)
+
+/label ~suggestion
\ No newline at end of file

.gitlab/merge_request_templates/Default.md

+Summary
+
+(Summarize the content of the merge request)
+
+
+Relevant issue(s) fixed
+
+(list all issues fixed by that merge request if any)