Add third party alert

What does this MR do and why?

The Code Suggestions feature recently changed its default from first-party to third-party powered (Google Codey model). Users who originally enabled the feature did so assuming it was first-party powered and need to be made aware of the switch from a legal perspective now that the feature will be leveraging a third party to provide code suggestions on users' proprietary code.

Screenshots or screen recordings

Latest alert copy changes
root page
group page
project page

How to set up and validate locally

bin/rails c

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

• Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
• Sign in. Create group. Enable code suggestions and third party AI for that group
• Disable code suggestion for a user
• Visit group page. Make sure there is no third party alert.
• Enable code suggestion for a user
• Visit root page. Make sure there is no third party alert.
• Visit group page. Make sure there is a third party alert.
• Dismiss it. Make sure it stays dismissed.

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 #414965