Prefer rich text versions of project files in nav links

What does this MR do?

Given rich text and plain versions of CHANGELOG and CONTRIBUTING prefer the rich text version for the links displayed above the project.

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

Whether the behaviour for link creation for README has changed. Closes #44323 (moved)

Why was this MR needed?

When displaying contribution guidelines for a project, the first available file is picked even if there are rich text versions available. See #44323 (moved)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

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

What are the relevant issue numbers?

Solves #44323 (moved)