This change allows to collect data for a diagnostic report. This can be
done either from the command line through the new `km-diag-report` tool,
or in `km-config` from the new `Support` tab that allows to generate the
report and then copy it to the clipboard or save as a file.
The diagnostic report contains installed browsers and their versions and
installation methods as well as the default browser. It checks for
browsers installed through apt (Ubuntu/Debian), snap, and flatpak.
The change also has an implementation for pacman (Arch Linux) and
dnf/yum (Fedora), although these have not been tested.
Fixes: #7784
