Add mode for non-reactive Kotlin Server to OpenAPI Generator

[mitasov-ra]

At the moment Kora OpenAPI Generator supports the following modes:

• 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)

As one can notice we lack non-reactive versions for kotlin_client and kotlin_server.

For small projects dealing with asynchronous programming is overkill. Please consider adding these modes.