### 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
:param initial_comment: message to send to slack. (templated)
    :type initial_comment: str
    :param filename: name of the file (templated)
    :type filename: str
    :param filetype: slack filetype. (templated)
        - see https://api.slack.com/types/file
    :type filetype: str
    :param content: file content. (templated)
    :type content: str
    """
    template_fields = ('channel', 'initial_comment', 'filetype', 'content')
    ui_color = '#44BEDF'
    def __init__(
        self,
        channel: str = '#general',
        initial_comment: str = 'No message has been set!',
        filename: str = None,
        filetype: str = None,
        content: str = None,
        **kwargs,
    ) -> None:
        self.method = 'files.upload'
        self.channel = channel
        self.initial_comment = initial_comment
        self.filename = filename
        self.filetype = filetype
        self.content = content
        self.file_params = {}
        super().__init__(method=self.method, **kwargs)
    def execute(self, **kwargs):