Custom labels not working in Airflow 2.3.3

[Pai-Hung-Cheng]

Hello,

We are currently using Airflow 2.3.3 and airflow-exporter 1.5.3.
It seems that we face the same issue as in #113.
Is there any solution for it?

On the other hand, since we are using Prometheus and Alertmanager to monitor Airflow with this exporter,
is it possible for "airflow_dag_run_duration" metric to add 'owner' label, so that we can get dag owner to send alert email while alerting.

Thank you for your contribution!
Best Regards