Resolve "Design comments do not render the blockquotes correctly"

What does this MR do?

This MR adds back a md class removed on !41686 (merged) so markdown could be rendered properly

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Issue #250350 (closed)