Geo: Support GitLab Pages access control on secondaries
## Problem
After https://gitlab.com/gitlab-org/gitlab-ee/issues/9337 or https://gitlab.com/gitlab-org/gitlab-pages/issues/195, Pages access control would not work out of the box.
## Possible solution
- [ ] Have secondary GitLab Pages use the primary for OAuth.
## Acceptance criteria
- [ ] An admin can enable Pages access control on a primary and secondary
- [ ] When Pages access control is enabled, a logged-out user can view a public Pages site
- [ ] When Pages access control is enabled, a logged-out user cannot view a private Pages site
- [ ] When Pages access control is enabled, a project member can view a private Pages site
- [ ] When Pages access control is enabled, and a private Pages site was turned public, an anonymous user can view it
- [ ] When Pages access control is enabled, and a public Pages site was turned private, an anonymous user cannot view it
- [ ] A developer can find documentation for how to get this working
- [ ] Open any follow up issues
issue