adding support for getting list of foreign tables for PostgreSQL (#3856)
adding support for getting list of foreign tables for PostgreSQL (#3856)

* adding support for getting list of foreign tables for PostgreSQL

* need extra newline to pass lint

airbnb/caravel,apache/incubator-superset,mistercrunch/panoramix,dmigo/incubator-superset,zhouyao1994/incubator-superset,timifasubaa/incubator-superset,alanmcruickshank/superset-dev,airbnb/superset,timifasubaa/incubator-superset,airbnb/superset,airbnb/superset,airbnb/caravel,dmigo/incubator-superset,zhouyao1994/incubator-superset,apache/incubator-superset,airbnb/superset,apache/incubator-superset,airbnb/caravel,dmigo/incubator-superset,alanmcruickshank/superset-dev,mistercrunch/panoramix,mistercrunch/panoramix,timifasubaa/incubator-superset,zhouyao1994/incubator-superset,timifasubaa/incubator-superset,alanmcruickshank/superset-dev,airbnb/caravel,dmigo/incubator-superset,alanmcruickshank/superset-dev,mistercrunch/panoramix,zhouyao1994/incubator-superset,apache/incubator-superset,zhouyao1994/incubator-superset,apache/incubator-superset