Refactor Discovery STI to Facets
Discovery as a STI is limiting (e.g. previously discovered host blocks creating New Host with the same MAC address) and the STI code is complicated, particularly the code behind reusing New/Edit Host form (org/loc selectors, NIC configurations).
With introduction of Facets, we should be able to move away from STI.
We should consider also moving off the Hosts table into separate model, because users also want more complex auto-provisioning which is not feasible with reusing the Edit Host form (#13847).