Move AiGenieChat into GitLab chat

What does this MR do and why?

This is the final leg of changes in the course of https://gitlab.com/gitlab-org/gitlab/-/issues/410108+

This MR brings the AiGenieChat component into the GitLab chat (Tanuki Bot) to complete the consolidation of the chat interfaces and have a SSOT for any chat and chat-like interactions in the product.

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Follow the instructions in https://docs.gitlab.com/ee/development/ai_features.html#test-ai-features-locally
• Check Ask GitLab Chat (from Help menu in the left navigation):

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 #410108