GitLab Pages: new guides

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/28097 closes https://gitlab.com/gitlab-org/gitlab-ee/issues/994 closes https://gitlab.com/gitlab-org/gitlab-ce/issues/28098 closes https://gitlab.com/gitlab-org/gitlab-ce/issues/28190

New guides for GitLab 8.17 - bringing Pages to CE

• Pages index: /doc/pages/index.md
  • GitLab Pages from A to Z
    • Part 1: Static Sites, Domains, DNS Records, and SSL/TLS Certificates
    • Part 2: Quick Start Guide - Setting Up GitLab Pages
    • Part 3: Creating and Tweaking .gitlab-ci.yml for GitLab Pages

TODOS

• Video tutorials (upload to YT and link) (Marcia):

  • Pages Admin (Matija)
  • Quick Start (Marcia)

• Check where else in the docs we need to point to the new index (Axil would you please check?)

  • User docs (CE and EE)
  • Admin docs (CE/EE)
  • Somewhere else?

Reviews:

• @axil
• @SeanPackham