Resolve "Add GitLab 17 banner to the homepage & duo page"

Step 1: What is changing in this MR?

• Adds navigation banner to every page of the site
• updates hero pill on duo page

Production	Review app
https://about.gitlab.com/	https://3714-banner.about.gitlab-review.app/
https://about.gitlab.com//gitlab-duo/	https://3714-banner.about.gitlab-review.app/gitlab-duo/

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.

Build Variables:

• Use Contentful Preview API

Closes #3714