[#62864394] User can browse Postgres databases
[#62864394] User can browse Postgres schemas
[#62864394] PostgresConnection works for postgres

 - Fix queries with gp specific requirements for pg
 - pg only and shared implementations live in PostgresLikeConnection with GreenplumConnection
   overriding when necessary
 - build fixtures for postgres host in PG_HOST/ test data source yml
 - duplicate most of the GreenplumnConnection tests
[#62864394] Dry up gp/pg connection specs

 - Pulls duplicate specs into 'a postgres-like connection' shared behavior
   when duplicated between the 2 connection types
[#62864394] Activities can be fetched for pg datasets

 - Define access for pg_table and pg_view
 - Re-record search cassettes due to fixture shuffling
[#62864394] User can browse/show pg datasets

 - Adds column mapping for pg datasets
 - Some functionality remains to be enabled in the ui
[#62864394] Re-record search cassettes