**Description**
In the trigger page, there is a text area to enter (optional) conf json. It would be great if a sample JSON can be provided programatically while defining DAG

**Use case / motivation**

This will improve usability of the UI that triggers a DAG

tests/www/test_views.py
DAG_ID = 'dag_for_testing_log_view'
    DAG_ID_REMOVED = 'removed_dag_for_testing_log_view'
    TASK_ID = 'task_for_testing_log_view'
    DEFAULT_DATE = timezone.datetime(2017, 9, 1)
    ENDPOINT = 'log?dag_id={dag_id}&task_id={task_id}&execution_date={execution_date}'.format(
        dag_id=DAG_ID, task_id=TASK_ID, execution_date=DEFAULT_DATE
    )
    def setUp(self):
        
        self.old_modules = dict(sys.modules)
        
        logging_config = copy.deepcopy(DEFAULT_LOGGING_CONFIG)
        current_dir = os.path.dirname(os.path.abspath(__file__))
        logging_config['handlers']['task']['base_log_folder'] = os.path.normpath(
            os.path.join(current_dir, 'test_logs')
        )
        logging_config['handlers']['task'][
            'filename_template'
        ] = '{{ ti.dag_id }}/{{ ti.task_id }}/{{ ts | replace(":", ".") }}/{{ try_number }}.log'
        
        self.settings_folder = tempfile.mkdtemp()
        settings_file = os.path.join(self.settings_folder, "airflow_local_settings.py")
        new_logging_file = f"LOGGING_CONFIG = {logging_config}"
        with open(settings_file, 'w') as handle:
            handle.writelines(new_logging_file)
        sys.path.append(self.settings_folder)