Include CSP in the policy hierarchy

What does this MR do and why?

When a group is designated as a CSP group, it is included in the hierarchy of all_security_orchestration_policy_configurations.

This is the first step behind a feature flag to ensure that CSP policies are propagated to all groups and projects.

Feature flag can toggle this behavior for a specific group, or its the root ancestor group.

References

Screenshots or screen recordings

Before (or with FF disabled)	After

How to set up and validate locally

1. In rails console enable the feature flag

   Feature.enable(:security_policies_csp)

2. Create a top-level group and designate it as CSP:

   Security::PolicySetting.instance.update! csp_namespace: Group.find(<group_id>)

3. In the group, create a few security policies
4. Create another top-level group
5. Visit Secure -> Policies and verify that CSP policies are shown as well

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Related to #541510 (closed)