Add CronJob which cleans up the Airflow database in airflow helm chart

[kimminw00]

There is only cron job which cleans up pods.
But there is no CronJob which cleans up airflow database.
If CronJob which cleans up the Airflow database is added in airflow helm chart, it will be much more convenient to manage airflow clusters.

[potiuk]

Feel free to add it.

[potiuk]

Just to add - Airflow is created by > 2500 contributors - and most of them became contributors because they added things that they thought are useful for them (and also others). Seems like adding such a job is (and if you could test it for your case locally even better) is a great way to become one of the contributors and give back for the free software (and help the whole community).