Improved commit message body rendering

What does this MR do?

improved commit message body rendering

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

https://gitlab.com/gitlab-org/gitlab-ce/issues/41283

Screenshots (if relevant)

• A) Repository (at top of file tree)
• B) Repository > Commits list
• C) Repository > Commits > Commit detail
• D) Merge requests > Merge request detail (“Commits” tab)
• E) CI/CD > Pipelines > Pipeline detail
• F) New empty merge request (select source and target branches)

A,F

Before	After

B,D

Before	After

C,E

Before	After

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?