Fix discriminator override for kotlin

[altro3]

Fixed #1881

The same problem for kotlin generator.

Also minor improvements for generated kotlin code

[altro3]

@sdelamo You're a bit hasty with the release, I fixed the problem with override in Java, but forgot about Kotlin.

In general, it would be desirable to merge this fix as well, because now the problem persists with the generator for Kotlin. Maybe release 6.13.3?

[altro3]

@sdelamo ping

[matadini]

@altro3 @sdelamo

Hi I'm asking here because I don't know where I could do this, so: When do you plan to release a new version of the micronaut-gradle-plugin that will include fix https://github.com/micronaut-projects/micronaut-openapi/issues/1881? After merging kotlin fix? Or do you have any particular roadmap?

I'm asking because it is important for me from the perspective of developing an application for a client.

[altro3]

@matadini You don't need to wait for a fix for Kotlin, the fix for Java is already merged and included in the 6.13.2 release.

To use the latest version of micronaut-openapi in the gradle plugin, just write this:

micronaut {
    openapi {
        version = "6.13.2"
        client(file("swagger.yml")) {
              ...
        }
    }
}