docs: def _load_upgrades(self, remove_applied=True):
          """Load upgrade modules.
  
          :param remove_applied: if True, already applied upgrades will not
              be included, if False the entire upgrade graph will be
              returned.
          """
          if remove_applied:
              self.load_history()
  
          for entry_point in iter_entry_points('invenio_upgrader.upgrades'):
              upgrade = entry_point.load()()
              self.__class__._upgrades[upgrade.name] = upgrade
  
          return self.__class__._upgrades