Add group-level Pages access control enforcement
What does this MR do and why?
This MR introduces a group-level functionality to enforce Pages visibility access controls. When enabled, all group projects will be updated to no longer be public, making them restricted to project members.
This addresses #254962 and creates a sense of parity for GitLab.com group owners, as this feature already exists for SM Administrators at an instance level.
How does this work? Does it override the project's set visibility level?
This doesn't directly modify a project's visibility level. When we do checks to determine if a project is public or not, this will perform a relevant lookup and block public access. When the group setting is disabled, all project visibility levels return to their original state.
References
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Screenshots or screen recordings
Group-level setting
Walkthrough Video
How to set up and validate locally
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