Set and track ML doc changes

As a developer
I want to set and track ML-changed proprieties
So that I can use ML content on documents without losing that context

Details 

There are several occasions that we might want to change content on behalf of Machine Learning. For instance, in auto-fill and auto-correct use cases, we want to use ML suggestions as content.

This means when modifying a document, the audit must reflect that it wasn't a user doing a modification.
Also, because we might need to backtrack the edit, the previous value must be stored. In the case of auto-fill the previous value is really the default value for the field.

Finally, we need to easily track which content was changed by ML. This information needs to be usable via nxql.
This tracking data should also be available on the document entity json or as an enrichment from the rest API.