Added Code Suggestions Beta Alert

What does this MR do and why?

Implements #412300 (closed).

Adds Code Suggestions Beta Alert to gitlab.com.

Screenshots or screen recordings

Page	Sreenshots
Group
Project

How to set up and validate locally

1. Setup to simulate SaaS and restart GDK
2. Enable feature flag with Feature.enable :code_suggestions_alert in rails console
3. visit any group or project pages that the current user has access to

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 #412300 (closed)