GitLab Pages dev doc has moved into gitlab repo

• Link to the merge request of the new page: gitlab!88067 (merged) for https://docs.gitlab.com/ee/development/pages/index.html

• Give the MR a descriptive title.

• Link to the merge request that introduced the new page.

Related

• Related to Add GitLab Pages development documentation (gitlab!88067 - merged)
• Related to Revamp gitlab-pages development docs (gitlab-pages#730 - closed)