[datasource editor] Add description and label fields (#6927)
[datasource editor] Add description and label fields (#6927)

* Add description field for columns

* Add label for metrics

zhouyao1994/incubator-superset,apache/incubator-superset,zhouyao1994/incubator-superset,airbnb/superset,mistercrunch/panoramix,apache/incubator-superset,zhouyao1994/incubator-superset,airbnb/caravel,zhouyao1994/incubator-superset,airbnb/superset,airbnb/caravel,mistercrunch/panoramix,mistercrunch/panoramix,airbnb/superset,airbnb/caravel,apache/incubator-superset,airbnb/superset,mistercrunch/panoramix,apache/incubator-superset,apache/incubator-superset,zhouyao1994/incubator-superset,airbnb/caravel