Add Arch Linux container support and integrate pacman into install utilities. New files: ct/archlinux.sh (container build/update script), install/archlinux-install.sh (install entrypoint), and json/archlinux.json (metadata). misc/install.func: detect_arch in detect_os, add pacman bootstrap, and implement pacman handlers for pkg_upgrade, pkg_install, pkg_remove, pkg_clean and package refresh; include openssh install path for pacman and provide a cleanup_lxc override to run pkg_clean. Enables creating/updating Arch Linux LXC containers and proper package manager handling.
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