kotlin: Update codegen templates to support struct enums

[svix-mman]

The API looks like this

val sourceIn = IngestSourceIn(
    name = "name",
    uid = "uuiidd",
    config = IngestSourceInConfig.Cron(
        CronConfig(
            contentType = "ads123",
            payload = "payload",
            schedule = "* * * * *",
        )
    ),
)
// read the payload field
if (sourceIn.config is Cron) {
    // smart cast
    println(sourceIn.config.cron.payload)
}

// without any enum fields
val sourceIn = IngestSourceIn(
    name = "name",
    uid = "uuiidd",
    config = IngestSourceInConfig.Genericwebhook,
)

ref: https://github.com/svix/monorepo-private/issues/9981

[svix-jplatte]

You should configure your editor to always write a final newline ;)

[svix-jplatte]

VSCode: "files.insertFinalNewline": true,

[svix-jplatte]

Guess I can insert that newline myself soon-ish..