This makes two changes to the HAProxy documentation:
1) Replaces the `reqadd` statements with `http-request set-header` statements, including a dynamic `X-Forwarded-Host`. Rationale is that this is cleaner (no manual adding of domain), and extensible to a multi-domain environment. Note that I have NOT tested the `:[port]` trick on this form of the command since I run on port 443.
2) Moves the `redirect scheme` from the backend to the frontend. I disagree with the logic of the commit (002275468a) that moved this to the backend - in a multi-backend environment, putting it in the frontend is cleaner, and in this simple config it makes no functional difference.
