[3.13] Datakit JSON < > XML node

## Jobs to be done (optional)

A customer can transform XML from the upstream to json for the client and vice versa using a Datakit node for this purpose with no extra libs required.

## Definition of done
Document the new node with examples + how-to if possible.


## Information
https://konghq.atlassian.net/browse/KAG-7805

## Due date (optional)
 3.13 GA.


## Size
M