DataOutputAgent RSS output's default `atom:link` contains `https://` when Huginn doesn't support https

<?xml version="1.0" encoding="UTF-8" ?>
<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
<channel>
 <atom:link href="https://192.168.1.171:821/users/2/web_requests/20/secret.xml" rel="self" type="application/rss+xml" />
 <atom:icon>https://192.168.1.171:821/favicon.ico</atom:icon>
[...]

This breaks some RSS readers (it broke Feeder for me since https://github.com/spacecowboy/Feeder/pull/1096) that change the URL based on this field.

Huginn doesn't (appear to?) support HTTPS out of the box without using a reverse proxy, so it should use http for the url by default.

Workaround: set template.self to the url using HTTP.