Airflow version 2.2.1 needs to be updated

[EvaSpitzer]

While updating the Backfill Composer to Airflow 2.5.1 we faced the issue that an error in the class GCSObjectsWithPrefixExistenceSensor leads to an failure of the DAG.

I think the fix would be to:

1. Update the .requirements.txt file to an later airflow version (2.5.1)
2. Change the deprecated delegate_to parameter to impersonation_chain.

delegate_to is not available anymore in the latest version --> https://airflow.apache.org/docs/apache-airflow-providers-google/stable/_api/airflow/providers/google/cloud/sensors/gcs/index.html

I created already a commit for this but I am not allowed to push to Unaflow :/