Update Taxonomy docs, add missing display_type(s), taxa field attributes, etc.

[cesarvarela]

These are the currently implemented types:

Documented:

https://github.com/responsible-ai-collaborative/aiid/blob/64a9def8c2fa22f618fa4dbfb75f8c651d064e66/mongo.md?plain=1#L149-L160

Some new taxonomy fields aren't documented either:

(dummy_fields, complete_from, etc.)

[cesarvarela]

There is an undocumented display_type: 'long_string' in GMF classifications.