add zio-json support to openapi-codegen

[oker1]

Added support for zio-json, generated code forward-compatible with scala3

[hughsimpson]

Stunning, can't tell you how pleased I am to see another lib get support. I'll take a look this weekend - although I lack approval power, I am fairly well-versed in this area.

[kciesielski]

@oker1 Thanks a lot for this contribution! I'm OK with merging this as soon as I make sure that the flaky tests aren't related.