feat: maas_machine support commissioning for discovered machines

[skatsaounis]

Currently, maas_machine expects the pxe MAC address as a required field and also tries to create machine entries when it is used. However there are cases when the MAAS operators either do not know the PXE MAC address or the machine has already been discovered and the create is bound to fail since MAC address defined in Terraform module is already in use.

• In case of knowing the PXE MAC Address and the machine has been discovered (New) commission should be used instead of create
• In case of knowing only the power parameters, provider should try to perform a boot on the machine with them (bound to fail create action with dummy PXE MAC address) and later on match the discovered (New) machine, by comparing the MAC power address. Finally, the dummy machine has to be deleted. From this point, PXE MAC address is filled and the process is the same as the first case.

By supporting the above use cases, maas_machine will fully support commissioning of machines.