Tanuki Bot - Help Menu Init

What does this MR do and why?

Broken off from: !117597 (merged)
Follow up MR: !117930 (merged)

This MR is work towards the Tanuki Bot - Chat initiative. This MR is the 1st MR and the goal of this MR is to initialize the Help Menu item and Backend logic to determine whether to show the "Ask the Tanuki Bot" button should appear.

This MR is behind two Feature Flags: Feature.enable(:openai_experimentation) and Feature.enable(:tanuki_bot)

Note: The UX review is currently happening for the entire feature rather than the chunks here: !117597 (merged)

Screenshots or screen recordings

Feature Enabled	Feature Disabled
Enabled	Disabled

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 Tanuki Bot link
4. Ensure it does nothing.

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.