[REQ] Kotlin sealed classes support

Is your feature request related to a problem? Please describe.

Hello,
It would be great to enable support of Kotlin sealed classes. Is it going to happen? As far I know, there is no way to do it with the current version of OAI.

Describe the solution you'd like

Kotlinx Serializer now supports sealed classes. So, from:

@Serializable
sealed class OperationErrorV1 {
    @Serializable
    data class InvalidField(val field: String, val value: String?): OperationErrorV1()
    @Serializable
    data class NotFound(val title: String, val description: String): OperationErrorV1()
    @Serializable
    data class Conflict(val title: String, val description: String): OperationErrorV1()
    @Serializable
    data class Internal(val message: String): OperationErrorV1()
    @Serializable
    data class Unknown(val message: String): OperationErrorV1()
}

We can get smth like:

"errors": {
                "type": "blablablaErrorV1.Operation",
                "errors": [
                    {
                        "type": "blablabla.OperationErrorV1.InvalidField",
                        "field": "applicationId",
                        "value": null
                    },
                    {
                        "type": "blablabla.OperationErrorV1.InvalidField",
                        "field": "test",
                        "value": "test"
                    },
                    {
                        "type": "blablabla.OperationErrorV1.Internal",
                        "message": "hello"
                    }
                ]
            }

Describe alternatives you've considered

Currently, I do generate default data classes from YAML. So, from smth like this:

OperationError:
      title: OperationError
      type: object
      properties:
        invalidField:
          $ref: '#/components/schemas/OperationInvalidFieldError'
        notFound:
          $ref: '#/components/schemas/OperationNotFoundError'
        conflict:
          $ref: '#/components/schemas/OperationConflictError'
        internal:
          $ref: '#/components/schemas/OperationInternalError'
        unknown:
          $ref: '#/components/schemas/OperationUnknownError'

I receive the following data class:

@Serializable
sealed class OperationErrorV1 {
    @Serializable
    data class InvalidField(val field: String, val value: String?): OperationErrorV1()
    @Serializable
    data class NotFound(val title: String, val description: String): OperationErrorV1()
    @Serializable
    data class Conflict(val title: String, val description: String): OperationErrorV1()
    @Serializable
    data class Internal(val message: String): OperationErrorV1()
    @Serializable
    data class Unknown(val message: String): OperationErrorV1()
}

Additional context

OAI generator version - 5.1.1

The issue names no files, tests, or entry points. Start by locating the Kotlin generator's model-generation entry point and current tests for Kotlin data classes; done means supporting the demonstrated sealed-class hierarchy while preserving existing generation behavior.