**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.logout()
        self.login(username='test_viewer', password='test_viewer')
        url = 'tree?dag_id=example_bash_operator'
        resp = self.client.get(url, follow_redirects=True)
        self.check_content_in_response('runme_1', resp)
    def test_refresh_failure_for_viewer(self):
        
        self.logout()
        self.login(username='test_viewer', password='test_viewer')
        resp = self.client.post('refresh?dag_id=example_bash_operator')
        self.check_content_in_response('Redirecting', resp, resp_code=302)
class TestTaskInstanceView(TestBase):
    TI_ENDPOINT = '/taskinstance/list/?_flt_0_execution_date={}'
    def test_start_date_filter(self):
        resp = self.client.get(self.TI_ENDPOINT.format(self.percent_encode('2018-10-09 22:44:31')))
        
        
        
        self.check_content_in_response('List Task Instance', resp)
class TestTaskRescheduleView(TestBase):