add a filter to anomaly detection

[bachng2017]

What

add some code to solve this issue re-data/re-data#392

How

We've tried to minimized the impact by just adding some code to utilize the anomaly_detector. The filter basically is based on re_data_z_score.time_window_end

Sample configuration that ignore anomaly for emailevent on Monday and Tuesday. Because only time_window_end is available for now in re_data_z_score, we shift a day for it.

      - name: emailevents
        description: email events
        config:
          re_data_monitored: true
          re_data_anomaly_detector: {'name': 'z_score', 'threshold': 3, 'filter': 'date_format(date_add(''day'',-1,z.time_window_end),''%a'') not in (''Mon'',''Tue'')'}
          re_data_time_filter: date_add('day',2,parse_datetime(cast(dt as varchar),'yyyyMMdd'))

Notes: If this approach is acceptable, adding time_window_start to re_data_z_score might be helpful.