About Settings panel logo handling

[Bastien Nocera <bnocera redhat com>]

Hello,

During the GNOME 41 development cycle, we made it easier for
distributors to provide their own icons to be shown in the About
Settings panel.

After the changes in those 2 merge requests:
https://gitlab.gnome.org/GNOME/gnome-control-center/-/merge_requests/985
https://gitlab.gnome.org/GNOME/gnome-control-center/-/merge_requests/1042
the panel will expect to read the LOGO variable in /etc/os-release and
will try to show, in order of preference, icons with those names:
    $LOGO-text-dark: icon with text when dark theme is used
    $LOGO-text: icon with text
    $LOGO-dark: default icon when dark theme is used
    $LOGO: default icon

It will be up to the distribution to set a reasonable value to the
LOGO variable in /etc/os-release, as well as install icons, either in
the hicolor icon theme, or more likely in $datadir/pixmaps or
$datadir/icons, either as SVG or PNG files.

Cheers