Write logic to combing workflow labels, IGs with nodes

Additionally, move the inventory-specific hacks of yesteryear
  into the prompts_dict method of the WorkflowJob model
  try to make it clear exactly what this is hacking and why

Correctly summarize label prompts, and add missing EE

Expand unit tests to apply more fields

adding missing fields to preserve during copy to workflow.py

Fix bug where empty workflow job vars blanked node vars (#12904)

* Fix bug where empty workflow job vars blanked node vars

* Fix bug where workflow job has no extra_vars, add test

* Add empty workflow job extra vars to assure fix

awx/api/serializers.py

@@ -3223,9 +3223,9 @@ class JobCreateScheduleSerializer(LabelsListMixin, BaseSerializer):
                     ret[field_name] = self._summarize(field_name, ret[field_name])
             for field_name, singular in (('credentials', 'credential'), ('instance_groups', 'instance_group')):
                 if field_name in ret:
-                    ret[field_name] = [self._summarize(singular, cred) for cred in ret[field_name]]
+                    ret[field_name] = [self._summarize(singular, obj) for obj in ret[field_name]]
             if 'labels' in ret:
-                ret['labels'] = self._summary_field_labels(obj)
+                ret['labels'] = self._summary_field_labels(config)
             return ret
         except JobLaunchConfig.DoesNotExist:
             return {'all': _('Unknown, job may have been ran before launch configurations were saved.')}

awx/api/views/__init__.py

@@ -3726,6 +3726,7 @@ class JobCreateSchedule(RetrieveAPIView):
             extra_data=config.extra_data,
             survey_passwords=config.survey_passwords,
             inventory=config.inventory,
+            execution_environment=config.execution_environment,
             char_prompts=config.char_prompts,
             credentials=set(config.credentials.all()),
             labels=set(config.labels.all()),