**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 = self.client.get('userstatschartview/chart/', follow_redirects=True)
        self.check_content_in_response('User Statistics', resp)
    def test_permissions_list(self):
        resp = self.client.get('permissions/list/', follow_redirects=True)
        self.check_content_in_response('List Base Permissions', resp)
    def test_viewmenus_list(self):
        resp = self.client.get('viewmenus/list/', follow_redirects=True)
        self.check_content_in_response('List View Menus', resp)
    def test_permissionsviews_list(self):
        resp = self.client.get('permissionviews/list/', follow_redirects=True)
        self.check_content_in_response('List Permissions on Views/Menus', resp)
    def test_home_filter_tags(self):
        from airflow.www.views import FILTER_TAGS_COOKIE
        with self.client:
            self.client.get('home?tags=example&tags=data', follow_redirects=True)
            self.assertEqual('example,data', flask_session[FILTER_TAGS_COOKIE])
            self.client.get('home?reset_tags', follow_redirects=True)
            self.assertIsNone(flask_session[FILTER_TAGS_COOKIE])
    def test_home_status_filter_cookie(self):
        from airflow.www.views import FILTER_STATUS_COOKIE
        with self.client:
            self.client.get('home', follow_redirects=True)
            self.assertEqual('all', flask_session[FILTER_STATUS_COOKIE])
            self.client.get('home?status=active', follow_redirects=True)
            self.assertEqual('active', flask_session[FILTER_STATUS_COOKIE])
            self.client.get('home?status=paused', follow_redirects=True)
            self.assertEqual('paused', flask_session[FILTER_STATUS_COOKIE])
            self.client.get('home?status=all', follow_redirects=True)
            self.assertEqual('all', flask_session[FILTER_STATUS_COOKIE])
    def test_task(self):