[BUGFIX] Use content-type:application/rss+xml for RSS feeds

Move configuration for page header to additionalHeader.5
3 jobs for 404-change-content-type-for-rss-feed-page-type-101 in 2 minutes and 37 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #13152
test:php

00:00:20

 
  Build
passed #13153
build

00:00:32

 
  Layout
passed #13154
layout

00:01:45