[DMN Designer] PMML support - Using a linked PMML inside the editor

Aim of this ticket is to extend https://issues.redhat.com/browse/KOGITO-2761, which introduced the possibility to add a PMML file as included model.
The missing part is to use an included PMML file editor inside DMN editor. The user case which consume PMML file is the following:

• In the Model tab of the DMN designer, select or create the decision node or business knowledge model node in which you want to invoke the PMML model and click the Edit icon to open the DMN boxed expression designer:
• Set the expression type to Function (default for business knowledge model nodes), click the top-left function cell, and select PMML.
• In the document and model rows in the table, double-click the undefined cells to specify the included PMML document and the relevant PMML model within that document: