**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
self.clear_table(models.Variable)
        super().tearDown()
    def test_can_handle_error_on_decrypt(self):
        
        self.client.post('/variable/add', data=self.variable, follow_redirects=True)
        
        Var = models.Variable  
        (
            self.session.query(Var)
            .filter(Var.key == self.variable['key'])
            .update({'val': 'failed_value_not_encrypted'}, synchronize_session=False)
        )
        self.session.commit()
        
        
        resp = self.client.get('/variable/list', follow_redirects=True)
        self.check_content_in_response('<span class="label label-danger">Invalid</span>', resp)
    def test_xss_prevention(self):
        xss = "/variable/list/<img%20src=''%20onerror='alert(1);'>"
        resp = self.client.get(
            xss,
            follow_redirects=True,
        )
        self.assertEqual(resp.status_code, 404)
        self.assertNotIn("<img src='' onerror='alert(1);'>", resp.data.decode("utf-8"))
    def test_import_variables_no_file(self):
        resp = self.client.post('/variable/varimport', follow_redirects=True)
        self.check_content_in_response('Missing file or syntax error.', resp)
    def test_import_variables_failed(self):