Add keyForType option to deserialization

[lostintime]

... to be able to get 'type' field value in deserialized object.

*There may be another way I didn't find to achieve this).

[SeyZ]

Not sure to understand the need of this? Can you clarify your use case @lostintime ?

[lostintime]

@SeyZ it may be useful if endpoint is accepting multiple input entity types, but if it look useless for you - feel free to drop it, not sure if I'm using this myself anymore )