Bug#910892: gdm3: greeter.dconf-defaults is confusing for users

[Jeremy Bicha]

Package: gdm3
Version: 3.30.1-1

Test Case
-------------
Users wants to disable the user list on the login screen.

They manage to find /etc/gdm3/greeter.dconf-defaults and uncomment the
disable-user-list=true line. Then they restart their computer.

The login screen doesn't start.

The Problem
------------------
Users also need to uncomment the [org/gnome/login-screen] line.

Ideally, we would do like /etc/gdm3/daemon.conf (on Ubuntu it's named
custom.conf) and have those header lines uncommented by default.

The only reason I hesitate is that I'd rather we not force users
through the modified conffile prompt. Is there a good way to avoid
that? Maybe this issue is important enough that it doesn't matter if
upgrading users see that prompt?

This was originally reported as https://launchpad.net/bugs/1724944

Thanks,
Jeremy Bicha