**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
with assert_queries_count(42):
            resp = self.client.get('/', follow_redirects=True)
        self.check_content_in_response('DAGs', resp)
    def test_doc_urls(self):
        resp = self.client.get('/', follow_redirects=True)
        if "dev" in version.version:
            airflow_doc_site = (
                "http://apache-airflow-docs.s3-website.eu-central-1.amazonaws.com/docs/apache-airflow/"
            )
        else:
            airflow_doc_site = f'https://airflow.apache.org/docs/{version.version}'
        self.check_content_in_response(airflow_doc_site, resp)
        self.check_content_in_response("/api/v1/ui", resp)
    def test_health(self):