Support byte of string format

[koxudaxi]

trafficstars

This PR supports byte of string format.

OpenAPI expects that byte is base64-encoded characters. https://swagger.io/docs/specification/data-models/data-types/#string

But, I don't know how do we treat encoded/decoded values like base64 in Pydantic. I opened this issue. However, the problem is not resolved yet. samuelcolvin/pydantic#692

Related issues

https://github.com/koxudaxi/datamodel-code-generator/issues/30

[kshramt]

https://github.com/pydantic/pydantic/issues/692 was resolved.

[ilovelinux]

Resolved in v2.0a4 (changelog), It isn't backported to v1.x.