OpenAPI Generator Kotlin Client & Server

[GoodforGod]

Features:

• Kotlin Sync Client and Sync Server added
• Existing modes API parameter breaking change

Closes (#170)

Mode parameter change:
Before

java_client - non-reactive Java client
java_server - non-reactive Java server
reactive_client - reactive Java client (Project Reactor)
reactive_server - reactive Java server (Project Reactor)
kotlin_client - reactive Kotlin client (Project Reactor + Coroutines)
kotlin_server - reactive Kotlin server (Project Reactor + Coroutines)

After

java_client - non-reactive Java client
java_server - non-reactive Java server
java_reactive_client - reactive Java client (Project Reactor)
java_reactive_server - reactive Java server (Project Reactor)
kotlin_client - non-reactive Kotlin client
kotlin_server - non-reactive Kotlin server
kotlin_coroutine_client - reactive Kotlin client (Project Reactor + Coroutines)
kotlin_coroutine_server - reactive Kotlin server (Project Reactor + Coroutines)