Update "view app" link for review apps to reflect website path changes

The "View app" button for review apps on upstream MRs (like this) can be configured to link directly to the page you updated in our MR.

Currently, if you've modified an _index.md page, it goes to the wrong spot (like https://new.docs.gitlab.com/upstream-review-mr-ee-178795/api/graphql/reference/_index/).

We need to adjust the route-map.yml file to work better with Hugo paths.

The Handbook's config looks pretty close to what we need: https://gitlab.com/gitlab-com/content-sites/handbook/-/blob/main/.gitlab/route-map.yml?ref_type=heads (except our content is in doc instead of content).

Not sure if we have a route-map file anywhere but gitlab, so we'll also want to check the other project repos (runner, operator, etc).

Timing-wise it probably makes the most sense to do this right after we launch the Hugo site.