Clone command in cli

[joepio]

Cloning a Resource means creating a copy and hosting it on your own Server. This can be useful in many cases - think about making changes to some external model (e.g. making an extra property required).

It makes sense to (by default) store a reference to the original. This property cloned-from should be a Resource Array, as cloning could also happen to cloned resources.

Edit: I think it's better to not make this part of the CLI, but of lib. This means we can also use it in a /clone endpoint. I think it may make sense to provide it as a method on Resource

[joepio]

related: https://github.com/ontola/atomic-data/issues/21