Support device restart or kexec as part of workflows

[chrisdoherty4]

Summary

When provisioning devices users inevitably need to restart the device (or kexec). To date, users achieve a restart through an action which can lead to incorrect status reporting on Workflows.

When the restart action is run it instructs the kernel to perform a system restart. The restart process races against the action exiting and Tink Worker reporting the action was successful. In the case of kexec, we rarely - if ever - see the action transition to a success state. This generally leaves workflows to timeout which is misleading for users.

This issue is to track the introduction of restart/kexec to workflows as a built in feature removing the need to include an action. Other proposals are welcome.

[dln]

We just ran into this when setting tinkerbell up. 😄

+1 for a specific "restart action", since that'll keep it OS independent as well.

[jacobweinstock]

We might want to also add a power off builtin.