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
"""Shows task instances."""
        dag_id = request.args.get('dag_id')
        dag = current_app.dag_bag.get_dag(dag_id)
        dttm = request.args.get('execution_date')
        if dttm:
            dttm = timezone.parse(dttm)
        else:
            return "Error: Invalid execution_date"
        task_instances = {ti.task_id: alchemy_to_dict(ti) for ti in dag.get_task_instances(dttm, dttm)}
        return json.dumps(task_instances, cls=utils_json.AirflowJsonEncoder)
class ConfigurationView(AirflowBaseView):
    """View to show Airflow Configurations"""
    default_view = 'conf'
    class_permission_name = permissions.RESOURCE_CONFIG
    base_permissions = [
        permissions.ACTION_CAN_READ,
        permissions.ACTION_CAN_ACCESS_MENU,
    ]
    @expose('/configuration')
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_CONFIG),
        ]
    )
    def conf(self):