Disable Debian non-free in APT in the ISO
Originally created by @intrigeri on #10130 (Redmine)
We need non-free for building (firmwares). But I don’t see a good reason to configure APT in a way that users may install non-free software without even noticing.
Except, perhaps, that if we disable non-free, users who actually want to
install stuff, in a persistent manner, from non-free, may need to do
crazy stuff (what exactly? would dotfiles work to drop stuff in
sources.list.d? alternatively, can we configure APT to use another
sources.list.d that users can make persistent?). Should this be
blocking us from addressing the aforedescribed problem?
Feature Branch: doc/10543-dotfiles-for-apt