Migrate Singularity example DAGs to new design #22464

There is a new design of system tests that was introduced by the AIP-47.

All current example dags need to be migrated and converted into system tests, so they can be run in the CI process automatically before releases.

This is an aggregated issue for all example DAGs related to Singularity provider. It is created to track progress of their migration.

List of paths to example DAGs:

• airflow/providers/singularity/example_dags/example_singularity.py