Externalize Postgres connection configs

Externalize all DB connection configs as environment variables.  To connect to a local database, either create environment variables for the following settings or add .env file:

- DB_HOST='localhost'
- DB_USER='\<db_user\>'
- DB_PASSWORD='\<db_password\>'
- DB_NAME='\<db_name\>'

@rstellar, @jjmerino, @kmeurer, @jamesongamble, @suprbh - please review and merge this pull request