Simplify static IP injection: use NMConnection file instead of systemd unit

Replace the shell script + systemd oneshot approach with a direct
NMConnection keyfile for enp1s0. This is simpler and matches how the
Assisted Installer handles static IPs on bare metal — configure-ovs.sh
already knows how to migrate a statically-configured NIC to br-ex.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>