Support `ror` for entities

[fkohrt]

Entities support the field ror as of citation-file-format/citation-file-format#484, so the following should be valid:

authors:
  - name: German Aerospace Center
    ror: https://ror.org/04bwf3e34
cff-version: 1.2.0
message: "If you use this software, please cite it using these metadata."
title: "My Research Software"

However, cffinit gives the following waring:

Could not add author. It is not a Person due to fields name, ror and not an Entity due to fields ror. Skipping.