Make koza able to handle yamls with multiple Source configurations

[DnlRKorn]

Here's an excalidraw I whipped up of the current Koza pipeline.

It may be desirable to make it so "transform.yaml" has two different configurations for two different writers/filters. I have a few ideas how we could do this;

1. One simple one may be just making a different yaml file and having two yaml files. This would include the least amount of rewriting.
2. Refactor "transform_source" into an entry point which converts the yaml file pointer into a koza.Source object and then another helper function which runs and processes koza.Source objects. Then write another function called "transform_sources" which does specialized processes on the yaml file to make multiple koza.Source objects.