Implement BigQueryReader

[criccomini]

We need a BigQueryReader to go along with our SnowflakeReader. The BQ Reader should use BQ's API client rather than querying information_schema (i.e. don't use DbapiReader), though. We get more robust data this way.

[criccomini]

This looks like it could be useful for testing:

https://github.com/goccy/bigquery-emulator

.. via https://stackoverflow.com/questions/59138674/google-bigquery-local-emulation