**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"
        ]
```

airflow/operators/email.py
self,
        *,
        to: Union[List[str], str],
        subject: str,
        html_content: str,
        files: Optional[List] = None,
        cc: Optional[Union[List[str], str]] = None,
        bcc: Optional[Union[List[str], str]] = None,
        mime_subtype: str = 'mixed',
        mime_charset: str = 'utf-8',
        **kwargs,
    ) -> None:
        super().__init__(**kwargs)
        self.to = to  
        self.subject = subject
        self.html_content = html_content
        self.files = files or []
        self.cc = cc  
        self.bcc = bcc
        self.mime_subtype = mime_subtype
        self.mime_charset = mime_charset
    def execute(self, context):