Fixes needed for the 2025 ICPC image

[nickygerritsen]

• Autologin to lightdm instead of gdm.
• Remove or fix dconf config.
• Import pc2 packages key, see below.
• Find a way to copy kotlin to chroot from /opt/kotlinc to /chroot/domjudge//usr/lib/kotlinc
• Stop the container-vscgallery.service service.
• Use openjdk-21-jdk-headless instead of openjdk-17-jdk-headless inside the chroot.
• Remove cgroup v1 config from kernel flags.
• Fix autostart for XFCE instead of gnome or install gnome terminal.
• Change wf46-domjudge and wf47-domjudge to be only domjudge in SSL certificate for the server.
• Fix DOMlogo start. Locally I used autostart again since the service didn't seem to work.

PC2 packages key import:

cat /etc/apt/trusted.gpg.d/pc2packages.asc | gpg --dearmor > ~/pc2.gpg
gpg --no-default-keyring --keyring /usr/share/keyrings/ubuntu-archive-keyring.gpg --import ~/pc2.gpg

For most I have local hacks, but we need to do this properly.