AIRFLOW-5492: added missing docstrings (#6107)
AIRFLOW-5492: added missing docstrings (#6107)

(cherry picked from commit 3c064d4416ae9b924f63dc136262b1d331615aa7)

owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow