**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
resp_json = json.loads(self.client.get('health', follow_redirects=True).data.decode('utf-8'))
        self.assertEqual('healthy', resp_json['metadatabase']['status'])
        self.assertEqual('unhealthy', resp_json['scheduler']['status'])
        self.assertIsNone(None, resp_json['scheduler']['latest_scheduler_heartbeat'])
    def test_home(self):
        with self.capture_templates() as templates:
            resp = self.client.get('home', follow_redirects=True)
            self.check_content_in_response('DAGs', resp)
            val_state_color_mapping = (
                'const STATE_COLOR = {"failed": "red", '
                '"null": "lightblue", "queued": "gray", '
                '"removed": "lightgrey", "running": "lime", '
                '"scheduled": "tan", "sensing": "lightseagreen", '
                '"shutdown": "blue", "skipped": "pink", '
                '"success": "green", "up_for_reschedule": "turquoise", '
                '"up_for_retry": "gold", "upstream_failed": "orange"};'
            )
            self.check_content_in_response(val_state_color_mapping, resp)
        self.assertEqual(len(templates), 1)
        self.assertEqual(templates[0].name, 'airflow/dags.html')
        state_color_mapping = State.state_color.copy()
        state_color_mapping["null"] = state_color_mapping.pop(None)
        self.assertEqual(templates[0].local_context['state_color'], state_color_mapping)
    def test_users_list(self):
        resp = self.client.get('users/list', follow_redirects=True)
        self.check_content_in_response('List Users', resp)
    def test_roles_list(self):
        resp = self.client.get('roles/list', follow_redirects=True)
        self.check_content_in_response('List Roles', resp)
    def test_userstatschart_view(self):