Python adjustments (#7809)

* #7797 Well Targets: Add scripting capability
* #7794 Python : Do not update childField or childFieldArray
* #7797: Python - Add scripting to well path collection
- Extend the pdmobject.py with method add_object()
- allow objects to be created from Python in well path collections
- add well targets to modelled well path

* #7795 Python : Make sure referenced generated classes are defined
* #7810 StimPlanModel: clean-up python generation
* Python : Always use empty string as default value for ptrFieldValue
It can happen that a ptrField is assigned to a pointer on object construction. (FaciesProperties) Make sure that constructor always assigns an empty string.

Co-authored-by: magnesj <magnesj@users.noreply.github.com>
Co-authored-by: Kristian Bendiksen <kristian.bendiksen@gmail.com>

GrpcInterface/RiaGrpcCommandService.cpp

@@ -269,7 +269,7 @@ void RiaGrpcCommandService::assignPdmObjectValues( caf::PdmObjectHandle*
                 }
                 else if ( childObjects.empty() )
                 {
-                    childObject = emplaceChildField( pdmChildFieldHandle );
+                    childObject = emplaceChildField( pdmChildFieldHandle, "" );
                 }
                 CAF_ASSERT( childObject );
                 if ( childObject )