Refactor pages_url to follow upstream changes

What does this MR do and why?

Failed pipeline:

• https://jihulab.com/gitlab-cn/gitlab/-/pipelines/1379840
• https://jihulab.com/gitlab-cn/gitlab/-/pipelines/1379282 ( appeared for the first time )

Changes from upstream: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/124886/diffs

Move GitLab Pages URL logic to a single place

How to fix:

refactor method in jh/app/views/projects/pages/_access.html.haml, which is referanced fromapp/views/projects/pages/_access.html.haml

Screenshots or screen recordings

non-ui

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