Allow passing json data when setting workflow variables in StartWorkflowOperation

Variables can be set on the new workflow by invoking this operation with a parameter 'properties' of type org.nuxeo.ecm.automation.core.util.Properties ( implements by default a HashMap<String, String>()).
For exemple:

stringVar=The Document Title
dateVar=@{org.nuxeo.ecm.core.schema.utils.DateParser.formatW3CDateTime(CurrentDate.date)}

But when trying to pass a variable of type StringList, the following exception is thrown:

Caused by: org.nuxeo.ecm.core.api.model.PropertyConversionException: Property Conversion failed from class java.lang.String to class [Ljava.lang.Object;:

Since NXP-13653 a new method was added , to set a list of properties based on their JSON representation:

setJSONProperties(CoreSession session, DocumentModel doc, Properties properties)

This should be used to set the workflow variables:

• will allow to set variables of complex types by submitting a json string and keeping the backward compatibility since the operation gets a parameter of type Map<String, String> ( properties). For example, in order to set a variable of type StringList:

    assignees = ["John Doe", "John Test"]
  

• no migration required on Studio side for existing chains, since until now only scalar types were supported ( = json representation by default)