Support fields for taxonomies

Hello! I'd love to be able to use this plugin to add fields to taxonomies. Is there any work in this direction?

No files, tests, or entry points are named. Start by reviewing how the plugin currently adds fields to posts, pages, custom post types, and users, then compare that with WordPress taxonomy APIs. Done would require a defined taxonomy-field design, supported taxonomy objects, and clear acceptance criteria.

Written by the indexing model from the issue text.