CheriABI desktop environment (experimental)

As of the 22.12 release, the installer has gained the option to install a desktop environment using the Mali Bifrost GPU on the Morello System-on-Chip. The option installs a basic desktop environment using KDE and Wayland compiled for CheriABI with the cheri-desktop package. It also installs a hybrid ABI Firefox web browser via the cheri-desktop-hybrid-extras package.