Allow disabling creation of new records in link fields

First off, thanks for Dato, I think it’s a fantastic product!

One improvement in my eyes would be to be able to configure a link field so that the button to add a new record does not show up (such as + New LinkedModel).

We use link fields a lot for presenting configuration options (basically as an enum alternative) and it does not make sense to have them there.

I know that we could create a role that does not have the rights to create new LinkedModel records in general, but we might wan to allow the creation (e.g. for admins), but still not allow it from the link field itself.