[Ban AI] Duo Preview Features Form for Top-level group or Admin

Context

This is part of a larger epic that gives admins more control over where AI is allowed in their organization.

Scope of this issue

This issue is to add the Duo Preview Features Form for Top-level group or Admin. If on self-hosted, only who this control for the admin. If on SAAS, this should show only on top level groups.

This checkbox is essentially an opt-in to beta/experimental AI features for the instance or whole group.

• Implement the section title: GitLab Duo preview features under the On/Off/Never on form
• Implement the checkbox with label: Turn on experiment and beta features
• Implement subtitle: By enabling these features, you accept the GitLab Testing Agreement
• Implement the link on GitLab Testing Agreement to https://handbook.gitlab.com/handbook/legal/testing-agreement/
• If Off or Never on is selected, this check becomes disabled. Hovering on the checkbox shows a tooltip with the title: Setting disabled and description: Setting unavailable When GitLab Duo is turned off, experiment and beta features cannot be turned on

Designs

⚠ Final designs and UI copy Figma ⚠

Image	Description
	All settings options (beta/experiment setting NOT available on subgroup, as described in this issue)
	Banner is shown when "Default off" radio button is selected
	Banner is shown when "Never on" radio button is selected
	Experiment and Beta checkbox becomes disabled with Tooltip when "Never on" radio button is selected
	User receives a confirmation via notice upon save, page reloads