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**Description**

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Make `MongoToS3Operator` `mongo_collection` parameter templated.

**Use case / motivation**

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This would allow for passing a templated mongo collection from other tasks, such as a mongo collection used as data destination by using `S3Hook`. For instance, we could use templated mongo collection to write data for different dates in different collections by using: `mycollection.{{ ds_nodash }}`.

**Are you willing to submit a PR?**

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Yes.

**Related Issues**

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N/A

tests/providers/amazon/aws/transfers/test_mongo_to_s3.py
def setUp(self):
        args = {'owner': 'airflow', 'start_date': DEFAULT_DATE}
        self.dag = DAG('test_dag_id', default_args=args)
        self.mock_operator = MongoToS3Operator(
            task_id=TASK_ID,
            mongo_conn_id=MONGO_CONN_ID,
            s3_conn_id=S3_CONN_ID,
            mongo_collection=MONGO_COLLECTION,
            mongo_query=MONGO_QUERY,
            s3_bucket=S3_BUCKET,
            s3_key=S3_KEY,
            dag=self.dag,
        )
    def test_init(self):
        self.assertEqual(self.mock_operator.task_id, TASK_ID)
        self.assertEqual(self.mock_operator.mongo_conn_id, MONGO_CONN_ID)
        self.assertEqual(self.mock_operator.s3_conn_id, S3_CONN_ID)
        self.assertEqual(self.mock_operator.mongo_collection, MONGO_COLLECTION)
        self.assertEqual(self.mock_operator.mongo_query, MONGO_QUERY)
        self.assertEqual(self.mock_operator.s3_bucket, S3_BUCKET)
        self.assertEqual(self.mock_operator.s3_key, S3_KEY)
    def test_template_field_overrides(self):