Update Developer Experience hero image

Step 1: What is changing in this MR?

Closes: https://gitlab.com/gitlab-com/marketing/digital-experience/buyer-experience/-/issues/3578

Adds new hero image to Contentful (needs to be published when merging) and adjusts styling.

Production	Review app
https://about.gitlab.com/developer-experience/	https://3578-devex-hero.about.gitlab-review.app/developer-experience/

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/	WIP
https://about.gitlab.com/ja-jp/	WIP
https://about.gitlab.com/pricing/	WIP
https://about.gitlab.com/ja-jp/pricing/	WIP
https://about.gitlab.com/sales/	WIP
https://about.gitlab.com/gitlab-duo/	WIP
https://about.gitlab.com/enterprise/	WIP
https://about.gitlab.com/platform/	WIP
https://about.gitlab.com/free-trial/	WIP

Build Variables:

• Use Contentful Preview API

Closes #3578