Add `Roles and Permissions` menu to group settings

What does this MR do and why?

Added Roles and Permissions menu to the top-level group in the group settings.

Changelog: changed

EE: true

Screenshots or screen recordings

How to set up and validate locally

1. Enable feature flag: echo "Feature.enable(:custom_roles_ui_saas)" | gdk rails console
2. Enable the Ultimate license in one of the groups. This is done going to /admin/groups select Edit on a top level group, and choose the Ultimate plan. For example, /admin/groups/flightjs/edit:

1. Go to https://gdk.test:3443/groups/flightjs/-/settings/roles_and_permissions

MR acceptance checklist

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