Add metrics dashboard templates for the standard selector

What does this MR do?

This adds .metrics-dashboard.yml example templates to the template selector in the standard editor from the repository view

#220178 (closed)

This needs the backend MR merged into master to get a green pipeline

Screenshots

Selecting the metrics-dashboard template	Selecting a metrics-dashboard template

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content