Enable public/non-public URL field

[fsalemi]

User story / feature request

Requesting the addition of a new column to dim_gtfs_dataset, that marks non-public feeds that we don't want to be published to the open data pipeline.

Acceptance Criteria

The URL that we don't want to be published to the open data pipeline can be filtered out.

Notes

This would be a categorical dichotomous filed (BOOLEAN) by the name of private_dataset that can be true or false.