Automatically discover oneOf for sealed classes in OpenAPI

[LarsSven]

Description

In Kotlin, imagine we have a class like this:

@Schema(
    oneOf = [InputResourceReference.Action::class, InputResourceReference.Assignment::class],
    discriminatorProperty = "type",
    discriminatorMapping = [
        DiscriminatorMapping(value = "action", schema = InputResourceReference.Action::class),
        DiscriminatorMapping(value = "assignment", schema = InputResourceReference.Assignment::class)
    ],
    properties = [
        SchemaProperty(name = "type", implementation = String::class),
    ]
)
@JsonTypeInfo(
    use = JsonTypeInfo.Id.NAME,
    include = JsonTypeInfo.As.PROPERTY,
    property = "type"
)
sealed class InputResourceReference {
    @JsonTypeName("action")
    data class Action(
        val stage: String,
        val job: String,
        val action: String,
        val resourceUri: URI,
    ): InputResourceReference()

    @JsonTypeName("assignment")
    data class Assignment(val uri: URI): InputResourceReference()
}

It would be nice if OpenAPI could automatically determine the oneOf field (and possibly even the discriminator, though that would be harder) since it can be easily determined for sealed classes.

Implementation ideas

Jackson already implements this as can be seen in the example, so it could serve as a reference.

[quarkus-bot]

/cc @EricWittmann (openapi), @MikeEdgar (openapi), @geoand (kotlin), @phillip-kruger (openapi)