[AIRFLOW-3966] Correct default bigquery_conn_id in BigQueryTableSensor

[ryanyuan]

Fix default conn for BigQueryTableSensor

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[mik-laj]

Other operators for GCP use google_cloud_default as a default connection id. Maybe we should go in this direction?

[Fokko]

Agree with @mik-laj :-)

[mik-laj]

I started working in this direction, but I did not have time to finish it. If you want, you can base your work on this change.
https://github.com/PolideaInternal/airflow/pull/42/files

[ryanyuan]

@mik-laj @Fokko Agreed.

@mik-laj Nice initiative for your changes. Will you have time to continue working on it? If not, I would love to take the whole task. Cheers.

[mik-laj]

@ryanyuan I am currently dealing with other changes. Feel free and take the code / task.

[ryanyuan]

@mik-laj Cool! 👍

[ryanyuan]

Close this PR and start working on AIRFLOW-3987 to unify all GCP connections.