old_contents: from armstrong.apps.content.models import Content
  from django.db import models
  
  
  class Article(Content):
      body = models.TextField()
  
new_contents: from armstrong.apps.content.models import Content
  from armstrong.core.arm_content.mixins.publication import PublishedManager
  from django.db import models
  
  
  class Article(Content):
      body = models.TextField()
  
      published = PublishedManager()
  
subject: add published to Article