Use data catalog to replace old dataset directory

[nickevansuk]

This repository contains a reference to the old dataset directory:

https://github.com/openactive/openactive.rb/blob/91678ae0f0e6dc2ef4a5fd243aa3522d7e0f7b64/lib/openactive/datasets.rb#L4C16-L4C65

It should instead port the logic from dataset-utils, spidering the various datasets from source.