Add support for tag new fields

[baywet]

A few new fields were added to the tag object:

• summary (string?)
• parent (OpenAPITagReference?)
• kind (string?)

These properties should be added to the Tag object, and it's serialization/deserialization should be implemented for 3.2.0

When downgrading to 3.1.0, properties should be serialized as extensions, with an x-oas- prefix.