Add pipeline archival setting back under a feature flag for GitLab.com rollout

Summary

As part of the phased rollout plan for enabling CI/CD Pipeline Archival on GitLab.com, the pipeline archival setting needs to be re-introduced behind a feature flag. This allows controlled, gradual enablement on GitLab.com while keeping the setting available for Dedicated and self-managed instances.

Background

The rollout plan specifies adding the feature back under a feature flag that is enabled by default but disabled on GitLab.com, to control the rollout and provide a quick rollback path if any issues arise.

Tasks

• Introduce a feature flag (e.g. ci_pipeline_archival_setting) that gates the pipeline archival admin setting
• Feature flag should be enabled by default (so Dedicated and self-managed are unaffected)
• Feature flag should be disabled on GitLab.com initially to allow controlled rollout
• Ensure the archival setting UI and API are hidden/no-op when the flag is disabled on an instance
• Add appropriate tests covering the flag-gated behaviour
• Document the feature flag in the codebase

Acceptance Criteria

• The pipeline archival setting can be toggled on GitLab.com via the feature flag without a code deployment
• Disabling the flag on GitLab.com effectively disables archival (rollback path)
• Dedicated and self-managed instances continue to work as before (flag enabled by default)

Related

• Enable pipeline archival on GitLab.com epic