install_arch: init pacman keyring on first boot

Creates a systemd service which executes these commands on first boot:

pacman-key --init

pacman-key --populate archlinux

Also it makes sure /etc/pacman.d/gnupg is not absent.

At last it removes /etc/machine-id to make sure systemd launches first
boot services.
2 jobs for pacman_keyring_init in 36 seconds (queued for 5 seconds)
Status Name Job ID Coverage
  Test
passed ansible-lint #39888

00:00:36

passed terraform-validate #39889

00:00:31