feat: Add gd enterprise waitlist updates

Step 1: What is changing in this MR?

PLEASE DO NOT MERGE YET

• Update coming soon button to Join waitlist in pricing - Contentful
• Update coming soon button to contact us in gitlab duo page (content changed in BE repo)
• Adds new waitlist page - Contentful

NOTE: We would need to publish all draft/changed in Contentful before merge

Production	Review app
https://about.gitlab.com/	https://feat-gd-enterprise-cards.about.gitlab-review.app/solutions/gitlab-duo-enterprise/waitlist/
https://about.gitlab.com/	https://feat-gd-enterprise-cards.about.gitlab-review.app/pricing/
https://about.gitlab.com/	https://feat-gd-enterprise-cards.about.gitlab-review.app/gitlab-duo/

This MR changes a couple of files for the following page:

Production	Review app
https://about.gitlab.com/	https://feat-gd-enterprise-cards.about.gitlab-review.app/solutions/gitlab-duo-pro/sales/

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

Related to https://gitlab.com/gitlab-com/marketing/digital-experience/buyer-experience/-/issues/3658