### 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
"""
        Used by the execute function. Allows templating on the source fields
        of the api_call_params dict before construction
        Override in child classes.
        Each SlackAPIOperator child class is responsible for
        having a construct_api_call_params function
        which sets self.api_call_params with a dict of
        API call parameters (https://api.slack.com/methods)
        """
        raise NotImplementedError(
            "SlackAPIOperator should not be used directly. Chose one of the subclasses instead"
        )
    def execute(self, **kwargs):
        """
        The SlackAPIOperator calls will not fail even if the call is not unsuccessful.
        It should not prevent a DAG from completing in success
        """
        if not self.api_params:
            self.construct_api_call_params()
        slack = SlackHook(token=self.token, slack_conn_id=self.slack_conn_id)
        slack.call(self.method, json=self.api_params)
class SlackAPIPostOperator(SlackAPIOperator):