spring5 webflux/spring boot 2.0 functional support for kotlin

[fanliming]

Description

Please add spring5 webflux / spring boot 2.0 functional support for kotlin.

spring Kotlin support

Swagger-codegen version

2.3

Suggest a fix/enhancement

built on a Reactive Streams API to run on top of non-blocking servers such as Netty, Undertow.

[wing328]

@fanliming thanks for the suggestion. May I know if you've time to contribute the enhancement? I can show you some good starting points.