**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
#
#
#
import datetime
import unittest
from unittest import mock
from airflow.models.dag import DAG
from airflow.operators.email import EmailOperator
from airflow.utils import timezone
from tests.test_utils.config import conf_vars
DEFAULT_DATE = timezone.datetime(2016, 1, 1)
END_DATE = timezone.datetime(2016, 1, 2)
INTERVAL = datetime.timedelta(hours=12)
FROZEN_NOW = timezone.datetime(2016, 1, 2, 12, 1, 1)
send_email_test = mock.Mock()
class TestEmailOperator(unittest.TestCase):