Add custom access denied page for ultimate trials in-app

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/171981



Merged-by: Scott de Jonge <sdejonge@gitlab.com>
Approved-by: Serhii Yarynovskyi <syarynovskyi@gitlab.com>
Approved-by: Roy Liu <rliu@gitlab.com>
Approved-by: Dzmitry (Dima) Meshcharakou <12459192-dmeshcharakou@users.noreply.gitlab.com>
Approved-by: Scott de Jonge <sdejonge@gitlab.com>
Reviewed-by: Dzmitry (Dima) Meshcharakou <12459192-dmeshcharakou@users.noreply.gitlab.com>
Reviewed-by: Duo Code Reviewer <duo-code-review-bot@gitlab.com>
Co-authored-by: Doug Stull <dstull@gitlab.com>