### Apache Airflow Provider(s)

slack

### Versions of Apache Airflow Providers

apache-airflow-providers-slack==3.0.0

### Apache Airflow version

2.1.4 (latest released)

### Operating System

Debian GNU/Linux 11 (bullseye)

### Deployment

Other Docker-based deployment

### Deployment details

_No response_

### What happened

Using a template string for `SlackAPIFileOperator.filename` doesn't apply the templating.

### What you expected to happen

`SlackAPIFileOperator.filrname` should work with a template string.

### How to reproduce

Use a template string when using `SlackAPIFileOperator`.

### Anything else

Re: PR: https://github.com/apache/airflow/pull/17400/files
In commit: https://github.com/apache/airflow/pull/17400/commits/bbd11de2f1d37e9e2f07e5f9b4d331bf94ef6b97

`filename` was removed from `template_fields`.  I believe this was because `filename` was removed as a parameter in favour of `file`.  In a later commit `file` was renamed to `filename` but the `template_fields` was not put back.  The documentation still states that it's a templated field.

### Are you willing to submit PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

airflow/providers/slack/operators/slack.py
self,
        channel: str = '#general',
        username: str = 'Airflow',
        text: str = 'No message has been set.\n'
        'Here is a cat video instead\n'
        'https://www.youtube.com/watch?v=J---aiyznGQ',
        icon_url: str = 'https://raw.githubusercontent.com/apache/'
        'airflow/main/airflow/www/static/pin_100.png',
        attachments: Optional[List] = None,
        blocks: Optional[List] = None,
        **kwargs,
    ) -> None:
        self.method = 'chat.postMessage'
        self.channel = channel
        self.username = username
        self.text = text
        self.icon_url = icon_url
        self.attachments = attachments or []
        self.blocks = blocks or []
        super().__init__(method=self.method, **kwargs)
    def construct_api_call_params(self) -> Any:
        self.api_params = {
            'channel': self.channel,
            'username': self.username,
            'text': self.text,
            'icon_url': self.icon_url,
            'attachments': json.dumps(self.attachments),
            'blocks': json.dumps(self.blocks),
        }
class SlackAPIFileOperator(SlackAPIOperator):