docs: def create_or_update(cls, object_version, key, value):
          """Create or update a new tag for a given object version."""
          assert len(key) < 256
          assert len(value) < 256
          obj = cls.get(object_version, key)
          if obj:
              obj.value = value
              db.session.merge(obj)
          else:
              obj = cls.create(object_version, key, value)
          return obj