Move ontology-term-usage into OAK

Nobody has claimed this yet.

https://github.com/INCATools/ontology-term-usage

Steps for implementation:

0. make sure you understand the OAK interface vs adapter/implementation interface
1. define a new interface TermUsageInterface
2. this will have a single method, get_term_usage
3. make a new data model, a simple one that has a TermUsage structure
4. spread the original OTU code across existing adapters, creating new ones where appropriate. We now have ubergraph too
5. Add a simple command `term-usage`. Note like all commands this will work on a single adapter
6. Write a wrapper command outside the main `runoak` CLI, this won't follow the runoak conventions of having a single backend, it will broadcast to all endpoints, choosing remote ones as default

This seems a lot but each step is small and this will ensure extensibility

Start by reviewing the OAK interface versus adapter/implementation interface, then inspect the original ontology-term-usage repository. Done means defining TermUsageInterface and its data model, distributing the functionality across adapters, adding the term-usage command, and providing the broadcast wrapper across endpoints.

Written by the indexing model from the issue text.