Run sysupdate from initrd

[pothos]

Current situation

For extensions from the the sysext-bakery one has to define an initial version to be deployed with Ignition because otherwise one would need to wait for the update timer to trigger to provision the latest version.

Impact

Verbose Ignition config with fixed versions that get outdated.

Ideal future situation

Align with upstream systemd on how to run systemd-sysupdate from the initrd to do an initial update run for all components (that also downloads missing images)

Implementation options

Currently one has to script it with a call to list all components and then loop to update each one. Best would be a new update-all subcommand.

Additional information