code: def import_apps_submodule(submodule):
      
      found_apps = []
      for appconfig in apps.get_app_configs():
          app = appconfig.name
          if import_module_or_none('{0}.{1}'.format(app, submodule)) is not None:
              found_apps.append(app)
  
      return found_apps
docs: Look for a submodule is a series of packages, e.g. ".pagetype_plugins" in all INSTALLED_APPS.