allow to not store null using a new Configuration.nonEncodeNull property

[zigzago]

Because we can't always add a NonEncodeNull annotation

[jershell]

Litote/kmongo#104

[jershell]

It is big trouble because annotation allows mark ObjectId field. We have two way destinate goal, use @Serializable(with = ObjectIdSerializer::class) or use @nonEncodeNull.
@ContextualSerialization lose field type and try to found by value

//// kotlinx/serialization/ContextSerializer.kt
    public override fun serialize(encoder: Encoder, obj: T) {
        val s = encoder.context.getContextualOrDefault(obj)
        encoder.encodeSerializableValue(s, obj)
    }

that make imposible get actual serializer by null value
I hope may be in next version of kotlinx.serialization they add possibility for fix it

[jershell]

Hm, in v0.13.0 I look on the point "Hide NullableSerializer, introduce '.nullable' extension instead". Need more time for research

[jershell]

@zigzago
As variant i can make nonEncodeNullableId property of configuration with @file:UseSerializers(ObjectIdSerializer::class) or another serializer determ. ContextSerializer is not impossible to support