read/write dmn-diagram builder as json

[jangalinski]

Once the diagram is build and stored as dmn-xml, the information present in the builder (condition-type, and/or) is lost.
To reuse builder declarations and have better interoperability and transperency, it would be great if we could read/write the current state of a builder from json.

Hint: Conditions and data types use interfaces and sealed classes, so the trick here is to use jackson type values to add the additional information for deSer to the classes.

Flaw: This will add a (compile time) dependency to the jackson annotations ... but jackson is already used for xml generation and spring boot (with jackson default) is a main target platform, so I am willing to sacrafice runtime independency here.)