### Summary

The [`filename` parameter docs](https://docs.ansible.com/ansible/latest/collections/ansible/builtin/apt_repository_module.html#parameter-filename) don't give enough info to tell how the file name is generated.

I believe my `repo: deb https://packagecloud.io/linz/prod/ubuntu/ {{ ansible_distribution_release }} main` is hanging indefinitely ~~, and I suspect this has something to do with the file name being a duplicate, resulting in a background prompt which is never printed or dismissed, but it's hard to tell based on the [code](https://github.com/ansible/ansible/blob/f3be331c9cb2f2c6edeb0bdf28a1e8a9681d727c/lib/ansible/modules/apt_repository.py#L235-L258)~~ (Based on copying the code into a Python interpreter it looks like the generated file name is `packagecloud_io_linz_prod_ubuntu.list`, which looks fine.).

### Issue Type

Documentation Report

### Component Name

lib/ansible/modules/apt_repository.py

### Ansible Version

```console
N/A
```


### Configuration

```console
N/A
```


### OS / Environment

N/A

### Additional Information

N/A

### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
found = False
        keyfiles = ['/etc/apt/trusted.gpg']  
        for other_dir in APT_KEY_DIRS:
            
            keyfiles.extend([os.path.join(other_dir, x) for x in os.listdir(other_dir) if not x.startswith('.')])
        for key_file in keyfiles:
            if os.path.exists(key_file):
                try:
                    rc, out, err = self.module.run_command([self.gpg_bin, '--list-packets', key_file])
                except (IOError, OSError) as e:
                    self.debug("Could check key against file %s: %s" % (key_file, to_native(e)))
                    continue
                if key_fingerprint in out:
                    found = True
                    break
        return found
    
    def add_source(self, line, comment='', file=None):
        if line.startswith('ppa:'):
            source, ppa_owner, ppa_name = self._expand_ppa(line)
            if source in self.repos_urls:
                
                return
            info = self._get_ppa_info(ppa_owner, ppa_name)
            
            if not self._key_already_exists(info['signing_key_fingerprint']):
                
                keyfile = ''
                if not self.module.check_mode: