[nova][ironic][ptg] reconfigure the baremetal node through the resize API

ironic spec https://review.opendev.org/#/c/672252/

TODOs: * alex_xu (?) to create a nova spec to list possible alternatives about which nova REST API could be used to trigger reconfigure (resize, reboot, new api) * A potential way forward would be Ironic supporting resize (confirm/revert) as well with some magical autodetection of an Ironic instance *or* some magical flavor-based solution

Cheers, gibi