Set @AvroEnumDefault directly to the enum value instead of the class

[Chuckame]

Before:

    @Serializable
    @AvroEnumDefault("UNKNOWN")
    private enum class Enum {
        UNKNOWN,
        A,
        B,
    }

After:

    @Serializable
    private enum class Enum {
        @AvroEnumDefault
        UNKNOWN,
        A,
        B,
    }