Add async support for Amazon SNS Notifier

[ferruzzi]

Adds async support to the existing SNS Notifier so it can be used as an AsyncCallback for DeadlineAlerts, among other things

dags used for manual testing:

from datetime import datetime, timedelta

from airflow.providers.amazon.aws.hooks.sns import SnsHook
from airflow.providers.amazon.aws.notifications.sns import SnsNotifier
from airflow.sdk import task, DAG
from airflow.sdk.definitions.deadline import DeadlineAlert, DeadlineReference, AsyncCallback

PAST_DATE = datetime(1980, 8, 10, 2)
MSG_PREFIX = "SNS Testing Rnd 1:"

DEFAULTS = {"target_arn": << REDACTED >>, "message": "testing via Airflow"}


def _sns_callback(context):
    SnsHook().publish_to_target(**DEFAULTS, subject=f"{MSG_PREFIX} Hook as Callback -- {context['dag_run'].dag_id}")


@task
def send_sns_message(subject):
    SnsHook().publish_to_target(**DEFAULTS, subject=subject)


@task.bash(task_id='sleep_task')
def sleep_n_secs(seconds):
    return f'sleep {seconds}'


with DAG(
    "sns_hook_via_taskflow",
    tags=["sns"]
):
    send_sns_message(subject=f"{MSG_PREFIX} Taskflow -- {{{{ dag_run.dag_id }}}} ")

with DAG(
    "sns_callback_on_success",
    on_success_callback=_sns_callback,
    tags=["sns"],
):
    sleep_n_secs(1)

with DAG(
    "sns_notifier_as_callback",
    on_success_callback=SnsNotifier(**DEFAULTS, subject=f"{MSG_PREFIX} Sync Notifier as callback -- {{{{ dag_run.dag_id }}}} "),
    tags=["sns"],
):
    sleep_n_secs(1)


with DAG(
    "sns_notifier_as_deadline",
    deadline=DeadlineAlert(
        reference=DeadlineReference.FIXED_DATETIME(PAST_DATE),
        interval=timedelta(0),
        callback=AsyncCallback(
            SnsNotifier,
            kwargs={**DEFAULTS, "subject": f"{MSG_PREFIX} Async Notifier as Deadline -- {{{{ dag_run.dag_id }}}} "}
        ),
    ),
    tags=["sns"],
):
    sleep_n_secs(1)

and proof of delivery with working templating

CC: @ramitkataria @seanghaeli

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