Remove special spacing characters

What does this merge request do and why?

• Remove special spacing characters M-BM- (see collapsed section below)
• Fix long lines and use standard markup for comments <!-- --> (double dashes)

❯ cat -ve .gitlab/issue_templates/Default.md 
<!---$
Please read this!$
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Before opening a new issue, make sure to search for keywords in the issues:$
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- https://gitlab.com/gitlab-org/modelops/applied-ml/code-suggestions/prompt-library/-/issues$
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and verify the issue you're about to submit isn't a duplicate.$
--->$
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## Problem to solve$
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<!-- What problem do we solve? TryM-BM- toM-BM- defineM-BM- theM-BM- who/what/whyM-BM- ofM-BM- theM-BM- opportunityM-BM- asM-BM- aM-BM- userM-BM- story.$
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ForM-BM- example,M-BM- "AsM-BM- aM-BM- (who),M-BM- IM-BM- wantM-BM- (what),M-BM- soM-BM- IM-BM- canM-BM- (why/value)."$
-->$
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## Proposal$
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<!-- How are we going to solve the problem? -->$
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## Further details$
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<!-- Include examples, use cases, benefits, goals, or any other details that help us understand the problem better. -->$
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## Links / references$
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/label ~"group::ai model validation" ~"devops::ai-powered" ~"Category:Code Suggestions"$
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<!-- Select a type -->$
<!-- /label ~"type::bug" -->$
<!-- /label ~"type::feature" -->$
<!-- /label ~"type::maintenance" -->$

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• [-] Tests added for new functionality. If not, please raise an issue to follow up.
• [-] Documentation added/updated, if needed.