Create a xwiki-recommended list for Debian packages

The migration notes on https://www.xwiki.org/xwiki/bin/view/XWiki/Maintenance/Migrations/ are mentioning a

sudo wget "https://maven.xwiki.org/stable/xwiki-recommended.list" -P /etc/apt/sources.list.d/

which doesn't exist right now: we only support stable and LTS in our script (https://github.com/xwiki/xwiki-dev-tools/blob/master/debian/xwiki_scanpackages.sh).
It would be useful to add this recommended list (or any other name) to perform package upgrades.