Tanuki Bot - Rename UI to GitLab Chat

What does this MR do and why?

UI Change for https://gitlab.com/gitlab-org/enablement-section/tanuki-bot/-/issues/27
Slack Message (internal only): https://gitlab.slack.com/archives/C05333631PT/p1682369541551639

This change aims to be as Minimally Invasive as possible when renaming this feature. We currently do not have a permanent name for the Feature and so we are opting to only rename the customer facing UI elements while the name is agreed/decided upon.

For now we will be calling this feature GitLab Chat in the UI.

Screenshots or screen recordings

	Help Menu	Drawer
Before
After

How to set up and validate locally

Setup:

• Ensure you are on GitLab Ultimate with a valid license
• Enable Feature Flags: Feature.enable(:openai_experimentation) and Feature.enable(:tanuki_bot)

1. Ensure the New navigation is enabled. You can enable it by clicking your User profile photo in the top right and toggle the switch
2. Click the help link in the bottom left of the new Sidebar navigation
3. Click Ask the GitLab Chat link
4. Ensure drawer slides out and the Title is GitLab Chat. There shouldn't be anything else in the Drawer in this MR.

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.