And also 1) revert an accidental commit to the main config file, and 2) port over some forgotten things to the main config file
Port https://github.com/vector-im/riot-web/pull/12008
None of this will work as it will need tweaking (at the very least I've not copied the origin migrator because that's had long enough) but these are files which already existed in their current state and so don't need re-reviewing.
