Replace toolbox with distrobox

The consensus on the matrix chat is that distrobox is better than toolbox as a container and development solution.

I've used them both on Fedora Silverblue (and its derivatives) and found that to be true.

mkosi.conf.d/99-packages-development.conf

@@ -15,7 +15,10 @@ Packages=base-devel
          llvm
          perf
          qemu-desktop
-         toolbox
+         podman
+         podman-docker
+         podman-compose
+         distrobox
          tree
          vim
          virt-manager

mkosi.postinst.chroot

@@ -143,6 +143,11 @@ flatpak config --unset languages
 
 mv /var/lib/flatpak / # we'll extract this and later mount it into place
 
+# Fetch latest distrobox config from the kde-linux-containers repo
+mkdir -p /usr/share/distrobox
+curl --output /usr/share/distrobox/distrobox.conf \
+  'https://invent.kde.org/api/v4/projects/19899/repository/files/distrobox.conf/raw'
+
 # Enable samba usershare
 cat <<- EOF >> /etc/samba/smb.conf
 [global]