Add third party feature link to toggle

What does this MR do and why?

Adds subtext to Code Suggestions toggles. Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/415103

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

	Before	After
user preferences
group permissions

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

How to set up and validate locally

bin/rails c

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

• Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
• Sign in. Visit a group. Check subtext an and enable code suggestions and third party AI for that group
• Check subtext an and enable code suggestion for a user

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.