Add a configuration option for Self-Managed to allow top-level CI group sharing

Release notes

Problem to solve

The biggest known limitation of agent functionality is GitLab agent for K8s ci_access sharing does not... (#377932 - closed)

We can not allow cross-level group sharing on GitLab SaaS, as top-level groups are typically different tenants. At the same time, this could be enabled for Self-Managed customers, and based on internal discussions it seems feasible.

Proposal

• Introduce a setting in the Admin area that enables cross-group CI sharing. This needs to be available only in Self-Managed instance.
  • Enabled on new installations, but disabled by default on upgraded installations.
• Allow CI group sharing by updating the clause in CiAccess::Finder.
  • We will need to conditionally add this WHERE clause based on the setting.

Intended users

• Priyanka (Platform Engineer)

Feature Usage Metrics

As having a checkbox checked/unchecked does not offer much insights into usage, no dedicated metrics will be added.

Does this feature require an audit event?

Yes. Changing the value should fire: cluster_agent_top_level_sharing with values of enabled | disabled