Ensure we can support cross-project queries in Airflow

[jklukas]

As discussed in https://bugzilla.mozilla.org/show_bug.cgi?id=1563742, we will be starting to migrate all derived tables into the shared-prod project, so there will be an interim period where we will have tables split between derived-datasets:telemetry and shared-prod:telemetry_raw. As we migrate, we will be providing views in derived-datasets:telemetry and shared-prod:telemetry to ensure a consistent and uninterrupted interface for users.

During the interim, we will have some queries in Airflow writing to derived-datasets and some to shared-prod, with perhaps needing to read from a different project than they're writing into. We should check that we understand how to express this in our Airflow dags and that our entrypoint script is able to support these scenarios.

[jklukas]

We are now doing this and have sufficient support while we transition.