Add dependency firewall setting pt2

What does this MR do and why?

This is MR2 in a series of MRs to add the Dependency Firewall feature settings toggle for beta. The first MR (!241400 (merged)) which must be merged first, added the namespace setting, and this MR adds the UI to control that namespace setting. This will allow admins to enable the dependency firewall in the top-level groups settings, and later subgroups/projects can use that to decide if the dependency firewall functionalities are available.

This setting toggle is only shown on top level groups, and only on .com right now (self-managed and dedicated will have an instance level toggle). Also only shows if the dependency_firewall_phase1 feature flag is turned on, and the licensed feature dependency_firewall is present.

As per the design specs, this settings toggle is being added to a new settings section titled 'Secure' which will also later include the secrets manager settings. For right now it only includes the dependency firewall setting toggle (and therefore is gated by the availability of this toggle as per above).

Will be adding a MR2.5 to incorporate the banner under the toggle with the banner conveying beta information seen in the designs, the docs link, and also to add in another design requirement "Instrumentation event fires on every flip. Audit event emitted on every flip". Then MR3 will implement utilization of this new namespace setting to gate functionality (all behind the feature flag).

References

https://gitlab.com/gitlab-org/gitlab/-/work_items/604179

Screenshots or screen recordings

SCREENSHOTS OF ADDED UI

SETTING DOES NOT APPEAR FOR SELF MANAGED OR FOR SUBGROUPS ON SAAS

FIGMA DESIGN

How to set up and validate locally

1. Enable the dependency_firewall_phase1 feature flag
2. Navigate to a top-level group (ensure your GDK is running in SaaS mode)
3. Confirm the Secure section shows up in the groups settings
4. Confirm the dependency firewall toggle on the Secure settings page is functional, and that it persists its value

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.