### Description

The stable REST API seems to be missing the functionality to delete a DAG. 
This would mirror clicking the "Trash Can" on the UI (and could maybe eventually power it)

![image](https://user-images.githubusercontent.com/80706212/131702280-2a8d0d74-6388-4b84-84c1-efabdf640cde.png)


### Use case/motivation

_No response_

### Related issues

_No response_

### 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
.group_by(_convert_to_date(session, DagRun.execution_date), DagRun.state)
            .order_by(_convert_to_date(session, DagRun.execution_date).asc())
            .all()
        )
        dag_states = [
            {
                
                
                'date': dr.date if isinstance(dr.date, str) else dr.date.isoformat(),
                'state': dr.state,
                'count': dr.count,
            }
            for dr in dag_states
        ]
        data = {
            'dag_states': dag_states,
            'start_date': (dag.start_date or DateTime.utcnow()).date().isoformat(),
            'end_date': (dag.end_date or DateTime.utcnow()).date().isoformat(),
        }
        doc_md = wwwutils.wrapped_markdown(getattr(dag, 'doc_md', None))
        
        data = htmlsafe_json_dumps(data, separators=(',', ':'))
        return self.render_template(
            'airflow/calendar.html',
            dag=dag,
            doc_md=doc_md,
            data=data,
            root=root,
            dag_model=dag_model,
        )