Feature: Implicit model dependencies

[feluelle]

It would be great if we could make dependencies implicit by matching function arguments names to model names instead of having to also define them explicitly via ref(...).

[binste]

Sounds good! It would not work for sources where one also needs to provide the source name but maybe we could fall back on matching by function arguments if there is no depends_on decorator and in that case, all function arguments must be named after models. If a depends_on decorator is present, it's used instead.

Not sure when I'd get to this as it's a nice-to-have but not an urgent fix. I'm open for a PR on this if anyone wants to pick it up.