Add missing route map access methods for review apps

What does this MR do and why?

Updates the review apps documentation to include all available methods for accessing route-mapped pages.

Previously, the docs only mentioned access from merge requests, but users can also access these links from commit pages and file views.

Changes made

• Clarified that route maps work for files matching mapping patterns.
• Added documentation for accessing route-mapped links from:
  • File views (through "View file @ [commit]").
  • Commit pages (for branch, regular MR, and merged results pipelines).
  • Comparison views.
• Added note explaining merged results pipeline behavior.

🔍 Review app link

https://docs.gitlab.com/upstream-review-mr-ee-197227/ci/review_apps/#route-maps

📚 References

Closes Follow-up from "Refactors review apps doc" (#527503 - closed)