Switch to systemd-networkd

During one of the last meetings the team decided to switch from ifupdown to systemd-networkd. This needs to implemented for Bookworm and above.

Supported cases

EC2, Generic with cloud-init

Plan: Enable hotplug in cloud-init (supported only for EC2, OpenStack and ConfigDrive, all others get only cold-plug by default)

cloud-init

No hotplug support either in cloud-init and/or the platform, all network related changes need reboot.

GCE, Nocloud

Plan: Setup a default .network file.