test_k8s: introduce a DAG querying another task status via the Airflow API

We also introduce a custom Airflow API client class wrapping the generated one, adding Kerberos authentication support, as all Airflow instances running in Kubernetes have kerberos auth enabled for the API.

Depends-On: https://gerrit.wikimedia.org/r/c/operations/deployment-charts/+/1098094 Signed-off-by: Balthazar Rouberol brouberol@wikimedia.org Bug: T380765