[nova][ironic] nova docs bug for ironic looking for an owner

While discussing some tribal knowledge about how ironic is the black sheep of nova compute drivers I realized that we (nova) have no docs about the ironic driver like we do for other drivers, so we don't mention anything about the weird cardinality rules around compute service : node : instance and host vs nodename things, how to configure the service for HA mode, how to configure baremetal flavors with custom resource classes, how to partition for conductor groups, how to deal with scaling issues, missing features (migrate), etc. I've opened a bug in case someone wants to get started on some of that information: https://bugs.launchpad.net/nova/+bug/1852446 -- Thanks, Matt