High-level interface via the Bioregistry

The `bioontologies` package has a very high-level interface for getting OBO graphs by prefix, since it can automatically look up the appropriate IRIs via its mappings to OBO Foundry.

```
import bioontologies

parse_results = bioontologies.get_obograph_by_prefix("go")
go_graph_document = parse_results.graph_document
```

This could be extended to OAK and also let you choose if you want the OWL, OBO, or OBO Graph JSON artifact to get consumed

Start with the existing bioontologies.get_obograph_by_prefix("go") interface and review how it resolves prefixes through OBO Foundry mappings. Then determine how OAK should expose the equivalent high-level interface and allow selecting OWL, OBO, or OBO Graph JSON artifacts; done means the supported artifact choices and interface behavior are defined and implemented.

Written by the indexing model from the issue text.