container vs host NetworkConfig

Consider the following modeling:
```
class host(MachineModel):
class container_1(MachineModel): pass
class container_2(MachineModel): pass
```
We almost certainly want different networking for host than for the two containers.
We presumably need to override a few other things including machine_implementation_key.

For PodmanContainer, PodmanPod and PodmanPodModel, we can introduce a different injection key that preferentially sets the NetworkConfig.
But that isn't as useful as it might appear because most netowrk_links are set on MachineModel not on the underlying machine.
Currently there is not a good way to handle this at the MachineModel level.