**Description**

Files are not part of the templated fields in the `EmailOperator` https://airflow.apache.org/docs/stable/_modules/airflow/operators/email_operator.html

Whle in fact file names should also be templated .

**Use case / motivation**
We want to store files accordingly to the DAGs execution date and further send them to email recipients like so:

```
send_report_email = EmailOperator(
        ....
        files=[
            "/tmp/Report-A-{{ execution_date.strftime('%Y-%m-%d') }}.csv",
            "/tmp/Reportt-B-{{ execution_date.strftime('%Y-%m-%d') }}.csv"
        ]
```

tests/operators/test_email.py
def setUp(self):
        super().setUp()
        self.dag = DAG(
            'test_dag',
            default_args={'owner': 'airflow', 'start_date': DEFAULT_DATE},
            schedule_interval=INTERVAL,
        )
        self.addCleanup(self.dag.clear)
    def _run_as_operator(self, **kwargs):
        task = EmailOperator(
            to='airflow@example.com',
            subject='Test Run',
            html_content='The quick brown fox jumps over the lazy dog',
            task_id='task',
            dag=self.dag,
            **kwargs,
        )
        task.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE)
    def test_execute(self):
        with conf_vars({('email', 'email_backend'): 'tests.operators.test_email.send_email_test'}):
            self._run_as_operator()
        assert send_email_test.call_count == 1