Triggering LegacyCheckpoint without 'validation_operator_name' from GreatExpectationsOperator

[ShaharPotash1]

@talagluck as I wrote on the Slack channel,
I'm trying to trigger a Slack notification with the GreatExpectationsOperator.
It necessary to use the validation_operator_name to trigger such notification and it is not possible with the current configuration:
https://github.com/great-expectations/airflow-provider-great-expectations/blob/e92a613db94aa872957fa8626f6d5e71690fe421/great_expectations_provider/operators/great_expectations.py#L130