Tech Debt: update deprecated settings values

[pbastia]

The latest Airflow upgrade had a few deprecation warnings:

/home/airflow/.local/lib/python3.8/site-packages/airflow/configuration.py:724 DeprecationWarning: The auth_backend option in [api] has been renamed to auth_backends - the old setting has been used, but please update your config.
/home/airflow/.local/lib/python3.8/site-packages/airflow/configuration.py:747 DeprecationWarning: The auth_backend option in [api] has been renamed to auth_backends - the old setting has been used, but please update your config.
/home/airflow/.local/lib/python3.8/site-packages/airflow/configuration.py:761 FutureWarning: The auth_backends setting in [api] has had airflow.api.auth.backend.session added in the running config, which is needed by the UI. Please update your config before Apache Airflow 3.0.
/home/airflow/.local/lib/python3.8/site-packages/airflow/models/dag.py:450 DeprecationWarning: The dag_concurrency option in [core] has been renamed to max_active_tasks_per_dag - the old setting has been used, but please update your config.
/home/airflow/.local/lib/python3.8/site-packages/airflow/models/dag.py:3854 DeprecationWarning: The dag_concurrency option in [core] has been renamed to max_active_tasks_per_dag - the old setting has been used, but please update your config.

These will need to be addressed before we update to a future version