Add ability to change Bigquery Host via configuration parameters

[ddcprg]

Hi,

I'm looking to use this connector and harness an integration test to make sure the connector config is correct before deploying the connector, kind of end to end test mocking the Bigquery endpoint. At the moment is impossible to achieve this as there is no way to configure the Bigquery host for the client. I was wondering if adding an undocumented or documented property for this would be useful and whether you think this could be included at all.

Cheers!