Add code suggestions UI

What does this MR do and why?

Adds a group based UI for controlling enrollment into the ai assisted web ide code suggestions using group

📓

• documentation MR !117029 (merged) is a dependency of this MR.
• design/etc as per #405126

Screenshots or screen recordings

How to set up and validate locally

1. Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
2. Enable the ai_assist_ui and ai_assist_flag

   Feature.enable(:ai_assist_ui)
   Feature.enable(:ai_assist_flag)

3. Create new top level group or use an existing.
4. Visit the admin path to edit the plan of the group such as: http://gdk.test:3000/admin/groups/non-owner-notification/edit
5. Update the plan to be Ultimate and Save

6. Visit the group's Settings -> General -> Permissions and group features
7. Find the Code Suggestions area and toggle/save the setting.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #405126