Follow-up from "Refactors review apps doc"

The following discussion from !185185 (merged) should be addressed:

• @marcel.amirault started a discussion: (+3 comments)

  I've been using review apps for almost 6 years, and this is the first time I noticed this feature! 😲

  It took me a few attempts to find these links though, it's not exactly intuitive, especially with merge requests! If you have merged results pipelines, you have to select the commit in the Pipelines tab, not any of the commits in the Commits tab. Merged results pipelines generate an internal commit to run the pipeline for (merging the MR's branch with the feature branch, to preview how it'll look when merged).

  I assume that with regular merge request pipelines (which can happen when there's a conflict in the MR) and branch pipelines, the commit from the Commits tab will work, but I'm not positive!

  So for example, with this MR, there's no review app link from the latest commit, and you can also see there's no pipeline associated with the latest commit:

  • 76a6dd5c

  But if you go to the pipelines list, and click on the latest pipeline's commit (currently 31ab6a30), you now see an extra icon on the right of doc/ci/review_apps/_index.md:

  • 31ab6a30

  From there, you can click on View file, and see the file and another review app link on the right:

  • https://gitlab.com/gitlab-org/gitlab/-/blob/31ab6a308964d1fdc6fd1f491cca53525d4221af/doc/ci/review_apps/_index.md

  This will be challenging to explain simply. Even the on-hover text is tricky to talk about, as it's dynamic: View on docs.gitlab.com/upstream-review-mr-ee-185185 🤔