### Description

In Airflow UI. If we go to Browse --> DAG Runs, then DAG Runs view will be displayed.

Table contains a lot of insightful values likes DAG execution date, Start date, end date, Dag config etc

Request to add DAG duration column in the same table.
DAG Duration i.e. DAG end_date timestamp  - DAG start_date timestamp

### Use case/motivation

Analytics purpose of knowing DAG duration at all DAGs level. So that I can easily find out which DAG  have least and max duration.

### Related issues

Checked open issues. There aren't any

### Are you willing to submit a PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

airflow/www/views.py
dag = dag.partial_subset(task_ids_or_regex=root, include_downstream=False, include_upstream=True)
        num_runs = request.args.get('num_runs', type=int)
        if num_runs is None:
            num_runs = conf.getint('webserver', 'default_dag_run_display_number')
        try:
            base_date = timezone.parse(request.args["base_date"])
        except (KeyError, ValueError):
            base_date = dag.get_latest_execution_date() or timezone.utcnow()
        with create_session() as session:
            dag_runs = (
                session.query(DagRun)
                .filter(DagRun.dag_id == dag.dag_id, DagRun.execution_date <= base_date)
                .order_by(DagRun.execution_date.desc())
                .limit(num_runs)
                .all()
            )
            dag_runs.reverse()
            encoded_runs = [wwwutils.encode_dag_run(dr) for dr in dag_runs]
            dag_run_dates = {dr.execution_date: alchemy_to_dict(dr) for dr in dag_runs}
            min_date = min(dag_run_dates, default=None)
            tis = dag.get_task_instances(start_date=min_date, end_date=base_date, session=session)
            data = {
                'groups': task_group_to_tree(dag.task_group, dag, dag_runs, tis),
                'dag_runs': encoded_runs,
            }
        
        return htmlsafe_json_dumps(data, separators=(',', ':'))
    @expose('/robots.txt')
    @action_logging
    def robots(self):