Break "Getting Started with GitLab Pages" in 4 instead of 3 guides
From Mark P.'s feedback on chat, starting here:
What
- Remove DNS and SSL sections from part 1 and put it on a new part 3
- Make part 3 = part 4
Why
- You don't need to know about DNS/SSL unless you want to add a custom domain, so it makes sense to come after part 2
- You don't need to dive into CI if you fork a template, so it makes sense to come as the last part
cc/ @axil @seanpackham @markpundsack