Assigning a preferred prefix

[cthoyt]

Now that there's a technical solution for storing preferred prefixes in the Bioregistry (#166 and #169) , there are few remaining things to discuss:

1. We need some guidelines on when/how people should add preferred_prefix annotations
2. Should we bulk import all OBO Foundry entries that implicitly just the OBO Foundry prefix, but capitalized (e.g., ones that omit the preferredPrefix field?)

[cthoyt]

Note on the second point - the OBO Foundry now requires all entries to annotate a preferred prefix, which gets propagated in the OBO Foundry import. Its still possible to override these, e.g., for entries like NCIT that have a corresponding ontology in OBO Foundry but aren't really OBO ontologies in the way that they're used