Concise enum definition with @SerialName fields

[vipulasri]

Kotlinx supports "@SerialName" for enums. We don't need custom serializers anymore.

This approach will output:

@Serializable
enum class Level(val value: String) {
    @SerialName("info") Info("info"),
    @SerialName("warning") Warning("warning");
}

[vipulasri]

@schani can you please review this PR? and also check why the "buildkite" pipeline is pending for all the recent PRs?