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