add text column to explain what the variable is used for

same as https://github.com/apache/airflow/issues/10840 just for Variables.


airflow/www/views.py
"""Autocomplete."""
        query = unquote(request.args.get('query', ''))
        if not query:
            wwwutils.json_response([])
        
        dag_ids_query = session.query(DagModel.dag_id.label('item')).filter(  
            ~DagModel.is_subdag, DagModel.is_active, DagModel.dag_id.ilike('%' + query + '%')
        )  
        owners_query = session.query(func.distinct(DagModel.owners).label('item')).filter(
            ~DagModel.is_subdag, DagModel.is_active, DagModel.owners.ilike('%' + query + '%')
        )  
        
        status = flask_session.get(FILTER_STATUS_COOKIE)
        if status == 'active':
            dag_ids_query = dag_ids_query.filter(~DagModel.is_paused)
            owners_query = owners_query.filter(~DagModel.is_paused)
        elif status == 'paused':
            dag_ids_query = dag_ids_query.filter(DagModel.is_paused)
            owners_query = owners_query.filter(DagModel.is_paused)
        filter_dag_ids = current_app.appbuilder.sm.get_accessible_dag_ids(g.user)
        
        dag_ids_query = dag_ids_query.filter(DagModel.dag_id.in_(filter_dag_ids))
        owners_query = owners_query.filter(DagModel.dag_id.in_(filter_dag_ids))
        
        payload = [row[0] for row in dag_ids_query.union(owners_query).limit(10).all()]
        return wwwutils.json_response(payload)