**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
content = '{"str_key": "str_value"}'
        with mock.patch('airflow.models.Variable.set') as set_mock:
            set_mock.side_effect = UnicodeEncodeError
            self.assertEqual(self.session.query(models.Variable).count(), 0)
            try:
                
                bytes_content = io.BytesIO(bytes(content, encoding='utf-8'))
            except TypeError:
                
                bytes_content = io.BytesIO(bytes(content))
            resp = self.client.post(
                '/variable/varimport', data={'file': (bytes_content, 'test.json')}, follow_redirects=True
            )
            self.check_content_in_response('1 variable(s) failed to be updated.', resp)
    def test_import_variables_success(self):
        self.assertEqual(self.session.query(models.Variable).count(), 0)
        content = (
            '{"str_key": "str_value", "int_key": 60, "list_key": [1, 2], "dict_key": {"k_a": 2, "k_b": 3}}'
        )
        try:
            
            bytes_content = io.BytesIO(bytes(content, encoding='utf-8'))
        except TypeError:
            
            bytes_content = io.BytesIO(bytes(content))
        resp = self.client.post(
            '/variable/varimport', data={'file': (bytes_content, 'test.json')}, follow_redirects=True
        )
        self.check_content_in_response('4 variable(s) successfully updated.', resp)
class PluginOperator(BaseOperator):