Allow the editing of authentications for a host

[skateman]

We have this feature already implemented for providers using assign_nested_authentication and this could be something similar. There are no endpoints assigned to the hosts, so it will be a little bit simpler. Most of the changes would be in the core, but as it changes the behavior of the API, I think the issue belongs here.

The current implementation is bumping into the same error as the zone endpoint.

@miq-bot add_label question
@Fryguy @abellotti @agrare

[NickLaMuro]

Just want to put this here for reference that general practice that we want to go with is being worked out and discussed in #916 so that PR should dictate how we decide to implement this feature, and that might not include using assign_nested_authentication.