Feat(Q): Initialize AmazonQ onboarding admin pages

• Feature branch: DRAFT: Amazon q spike (!174614 - closed)
• Parent MR: Feat(Q): Add AmazonQ db and config (!174949 - merged)
• Side note: This was originally developed in a private fork by GitLab team members in collaboration with Amazon's team.

What does this MR do and why?

This MR sets up the initial controller and views for GitLab Duo with Amazon Q. Please see the Feature branch MR for more context.

Screenshots or screen recordings

With feature flag enabled:

Admin > Settings	Admin > GitLab Duo	AmazonQ page

How to set up and validate locally

Prerequisites:

1. You'll need to make sure you have an Ultimate license and AI features setup on your GDK. See these instructions.

Instructions for these changes:

1. Enable the feature flag amazon_q_integration with Feature.enable(:amazon_q_integration) in a rails console
2. Visit Admin > Settings and look for GitLab Duo with Amazon Q section
3. Visit Admin > GitLab Duo and look for Amazon Q banner
4. Click Get started in the Amazon Q banner to see the stubbed out Amazon Q configuration page