UI: Poor UX for adding machine that's network booted into MAAS

MAAS version: 2.7.1 (8261-g.5143564e6)

One of the ways to add a new machine to MAAS is to set it to PXE boot. Assuming it's on a subnet where MAAS DHCP is running, and suitably configured, the machine will be added into MAAS and start gathering commissioning data.

When the machine finishes this commissioning, it will be in the 'New' state, with no power credentials setup. To move it into Ready, one needs to Commission, which in turn requires power credentials.

When going to 'Take Action', and Commission the MAAS UI correctly says that the machine cannot be commissioned without power credentials, but gives you no hint or direction as to where to do that.

Contrast against the 'Add hardware' journey where power credentials are part of the initial form.

Steps to reproduce:

1. Take an existing machine in MAAS, note it's power credentials.
2. Delete the machine in MAAS
3. Power on the machine using credentials from 1
4. Note the machine show up in Commissioning, wait for it to finish and land in New
5. Find the machine in machine listing, and go to Commission it.