Configure default terminal according to the kali desktop package installed

This is necessary in case more than one terminal is installed, and they
both have the same alternative priority.

For example, while installing all packages at once, sometimes apt will
resolve a dependency "x-terminal-emulator" to one of the many packages
that provide it, for example "zutty". And then it will also install the
terminal listed in the "kali-desktop-${desktop}" metapackage that is
selected, eg. "qterminal" for "kali-desktop-xfce".

Both zutty and qterminal have a alternative priority of 40 at the
moment, so if zutty gets unpacked first, it will have precendence and be
the default terminal.

It's a long-standing issue. By the past, We tried to make sure that the
default desktop terminal is installed first, by listing it early in the
dependencies of the "kali-desktop-{desktop}" metapackage, and it kind of
works with the debian-installer, but it was hard to make it work (we had
to do some changes in tasksel), and it's still brittle as it relies on
apt's dependency solving, which is apt's internal sauce and might change
(hint, apt will get a new solver soon, cf [1]).

As it turns out, it doesn't work for the live iso, somehow we still get
zutty taking precedence over qterminal, I didn't check why, it probably
has to do with how live-build constructs the apt command-line in order
to install everything.

In any case: I think our approach so far didn't work, so with this
commit, we take another approach: we set the default terminal from the
finish-install script, for both the installer iso and the live iso. That
should solve the issue for good.

[1]: https://blog.jak-linux.org/2024/05/14/solver3/

kali-config/common/includes.chroot/usr/lib/live/config/0031-kali-user-setup

@@ -31,6 +31,26 @@ configure_usergroups() {
     done
 }
 
+pkg_installed() {
+    dpkg -s "$1" 2>/dev/null | grep -q "ok installed"
+}
+
+configure_terminal() {
+    while read -r desktop terminal; do
+	pkg_installed kali-desktop-$desktop || continue
+	update-alternatives --verbose --set x-terminal-emulator /usr/bin/$terminal || true
+	break
+    done <<END
+e17   terminology
+gnome gnome-terminal.wrapper
+i3    kitty
+kde   konsole
+lxde  lxterminal
+mate  mate-terminal.wrapper
+xfce  qterminal
+END
+}
+
 # Avoid configuring multiple times in case persistence is enabled
 if [ -e /var/lib/live/config/kali-user-setup ]; then
     exit 0
@@ -39,11 +59,10 @@ fi
 # Set "kali" as password for the user kali
 usermod -p 'AqLUsDitNnTsw' kali
 
-# Change default shell to zsh
+# Apply various configuration
 configure_zsh
-
-# Add kali user to additional groups
 configure_usergroups
+configure_terminal
 
 # Remember that this script has been run
 touch /var/lib/live/config/kali-user-setup

kali-config/common/includes.installer/kali-finish-install

@@ -72,6 +72,28 @@ configure_usergroups() {
     done
 }
 
+pkg_installed() {
+    dpkg -s "$1" 2>/dev/null | grep -q "ok installed"
+}
+
+configure_terminal() {
+    while read -r desktop terminal; do
+	pkg_installed kali-desktop-$desktop || continue
+	echo "INFO: setting x-terminal-emulator alternative to '$terminal'"
+	update-alternatives --verbose --set x-terminal-emulator /usr/bin/$terminal || true
+	break
+    done <<END
+e17   terminology
+gnome gnome-terminal.wrapper
+i3    kitty
+kde   konsole
+lxde  lxterminal
+mate  mate-terminal.wrapper
+xfce  qterminal
+END
+}
+
 configure_sources_list
 configure_zsh
 configure_usergroups
+configure_terminal