feat: Add Gartner ai page

Build Variables:

• Use Contentful Preview API

Step 1: What is changing in this MR?

• Add new /gartner-mq-ai-code-assistants/ page for report release
• Updates banners in throughout the site
  • Gitlab duo pill
  • Top home banner

Production	Review app
https://about.gitlab.com/	https://feat-gartner-ai.about.gitlab-review.app/gartner-mq-ai-code-assistants/
https://about.gitlab.com/gitlab-duo/	https://feat-gartner-ai.about.gitlab-review.app/gitlab-duo
https://about.gitlab.com/	https://feat-gartner-ai.about.gitlab-review.app/

Step 2: Ensure that your changes comply with the following, where applicable:

• I, the Assignee, have run Axe tools on any updated pages, and fixed the relevant accessibility issues.
• These changes work on both Safari, Chrome, and Firefox.
• These changes have been reviewed for Visual Quality Assurance and Functional Quality Assurance on Mobile, Desktop, and Tablet.
• These changes work with our Google Analytics and SEO tools.
• These changes have been documented as expected.

Step 3: Ensure that your changes don't cause regressions on key pages, where applicable:

Production	Review app
https://about.gitlab.com/	https://feat-gartner-ai.about.gitlab-review.app/
https://about.gitlab.com/ja-jp/	https://feat-gartner-ai.about.gitlab-review.app/ja-jp
https://about.gitlab.com/pricing/	https://feat-gartner-ai.about.gitlab-review.app/pricing
https://about.gitlab.com/ja-jp/pricing/	https://feat-gartner-ai.about.gitlab-review.app/ja-jp/pricing
https://about.gitlab.com/sales/	https://feat-gartner-ai.about.gitlab-review.app/sales
https://about.gitlab.com/gitlab-duo/	https://feat-gartner-ai.about.gitlab-review.app/gitlab-duo
https://about.gitlab.com/enterprise/	https://feat-gartner-ai.about.gitlab-review.app/enterprise
https://about.gitlab.com/platform/	https://feat-gartner-ai.about.gitlab-review.app/platform
https://about.gitlab.com/free-trial/	https://feat-gartner-ai.about.gitlab-review.app/free-trial

Related to https://gitlab.com/gitlab-com/marketing/digital-experience/buyer-experience/-/issues/3970