Add BigQuery to Postgres transfer

[JoeSham]

Description
Hi, I suggest to add a BigQuery to Postgres transfer. There are currently 2 similar transfers already available: BigQuery to MySQL and BigQuery to MSSQL.
https://github.com/apache/airflow/tree/main/airflow/providers/google/cloud/transfers

Use case/motivation
To transfer data from BigQuery to Postgres

Related issues
Have not found any

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[potiuk]

Feel free to implement those.