[Docs] Represent the Airflow Python vs YML DAG feature better way

[pankajastro]

Maybe some script or pre-commit to check if the Python DAG feature vs YML DAG feature are in sync

[pankajastro]

Feedback from @matveykortsev to support notifications as callbacks.

Guys add please support for on_failure_callback in this way:

from airflow.providers.slack.notifications.slack import send_slack_notification
'on_failure_callback': [
send_slack_notification(
slack_conn_id='slack',
text="""
🔴 Task Failed.
Task: {{ ti.task_id }}
Dag: {{ ti.dag_id }}
Execution Time: {{ ti.execution_date }}
Log Url: {{ ti.log_url }}
""",
channel="analytics-alerts",
username="Airflow",
)
],
Now its only possible without params and only through absolute path for .py file

#206 (comment)