Hi there.\nI'm trying to add an api to superset.\nI have this code, and No errors starting superset but I get 404 when I try to access the api:\n```from flask_appbuilder.api import BaseApi, expose\nfrom superset.extensions import appbuilder\n\n\nclass ExampleApi(BaseApi):\n    @expose('/greeting')\n    def greeting(self):\n        return self.response(200, message="Hello")\n\n\nappbuilder.add_api(ExampleApi)```