Suggest that user-setup's list of groups in its
passwd/user-default-groups debconf template be moved (or copied) to
base-passwd.

This list does not currently seem to be available anywhere on an
installed Debian system. This makes it unncessarily hard to set up a
second (or perhaps first) desktop user in the right groups for
everything to work.

FWIW, I need it in a machine-readable form. So I've currently had to
make a copy of it, which will appear in the next update to propellor to
reach Debian.