Specific metrics for code on Banzai::Filter::SyntaxHighlightFilter

What does this MR do?

Add metrics for Rouge::Plugins::Redcarpet and Rouge::Formatters::HTMLGitlab

Why was this MR needed?

To try to understand why Banzai::Filter::SyntaxHighlightFilter is slow

What are the relevant issue numbers?

#18592 (closed)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• [ ] Documentation created/updated
• [ ] API support added
• Tests
  • [ ] Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together