Add support for target-bigquery

[XRyu]

Please add support for the Google BigQuery Target (as mentioned on Singer.IO: https://github.com/RealSelf/target-bigquery), would love to use this with KNOTS :)

[kndungu]

And we would love to give users the ability to use this with KNOTS :)

Due to bandwidth constraints we will not be able to work on this immediately. I am however writing up documentation on how to add taps and targets, this would enable anyone in the community to add them.

If it is something you're open to feel free to raise a PR adding BigQuery support once the documentation is up.