Add an example where we actively add config to dags with a policy

[krisgeus]

Would it make sense to also add an example where we actively add config to dags with a policy? Perhaps something like:

def task_assign_default_owner(task: BaseOperator):
    if not task.owner or task.owner.lower():
        task.owner = "baboon"

Originally posted by @danielvdende in https://github.com/godatadriven/whirl/pull/74#discussion_r927414417