Split data residency and HA content from GitLab Dedicated subscription page

What does this MR do and why?

This MR splits the data residency, available AWS regions, isolation, and availability and scalability content from the GitLab Dedicated subscription page.

Before: https://docs.gitlab.com/17.4/ee/subscriptions/gitlab_dedicated/index.html

After: https://main-ee-167975.docs.gitlab-review.app/ee/subscriptions/gitlab_dedicated/index.html and https://main-ee-167975.docs.gitlab-review.app/ee/subscriptions/gitlab_dedicated/data_residency_and_high_availability.html

Related issues

• #487370 (closed)
• technical-writing#1075
• gitlab-docs!5091 (merged)